I have a 2003 Jamis Eureka that I am thinking about converting to a semi-hybrid. I am looking for an inexpensive carbon fork, and more importantly a set of road bike wheels and tires. The bike is an 8-speed, and I am looking to spend 1-2 hundred dollars, with a maximum of 3 hundred. The bike is a 26", and if I am leaving something out, tell me. I am new to working on my bike and I don't know what I'm doing. Any help would be appreciated.

I checked, and found that the Jamis Eureka is, in fact, a mountain bike. Since this is so, it is designed to fit MTB rims which have a diameter of I believe 559mm (please, somebody let me know if I've got the number wrong), and road wheels have a diameter of 622mm. As you can see, that makes a difference of 63mm in diameter, or 31.5mm (about 1.25") difference in position of the rim inside the fork/stays.

Will your brakes allow you to move the pads an entire 1.25" upward (and inward, as well)? Of course they won't. Will a larger road wheel even fit inside the rear triangle? Probably not. Will you also cold-set the dropouts at the common 130mm for road wheels rather than leave them at the 135mm that MTB's usually are set at? If you find a road fork that will fit your frame, are you prepared to replace the brake lever that is designed for MTB linear-pull brakes with one designed to work with a road caliper?

Here's what's gonna happen-you'll waste $300 on a bunch of stuff that doesn't fit, you'll probably never get the rear brake installed, and in the end, you'll have a slow, heavy disaster with screwed-up handling (due to fitting a road fork onto a bike designed for a suspension), which will spend most of it's time sitting, because it's a lousy ride. If you have $300 to spend, there are a LOT of hybrids out there, complete, for that price on the used market.

What don't you like about your bike, and what are your riding goals? You have a mtn bike, and it sounds like you want to convert it so it is more like a road bike, but are you planning to just ride to get in shape, or is there a century in your plans?
Converting a mtn bike to be more like a road bike may be possible, but will usually cost more than getting an entry level or a used bike, and a converted mtn bike will still have 26" wheels. The cheapest options without buying a new bike will be to first evaluate your current gearing. You are probably under geared in that any down hill or a nice tail wind will cause you to spin out. So a change in your cassette should help with this. The next step would be to change your tires from a fat knobbie mtn tire to a slick 1.25 or 1.5 tire. This is the minimum you should do but you will still have suspension which isn't the most efficient on the road, and you have the mtn bike (upright) position which limits your hand positions and limits how aero you can get.
Let us know what your goals are and why you want to do this.

I'm not sure what that means, but it sounds like you just want to make your bike a bit more suitable for riding on pavement than it is now. If I have that right, here's what I suggest: get a pair of narrow slick tires. They will fit on your existing rims. You don't need to do anything else. You already have upright handlebars like a hybrid, you have shifters that work, etc.

Try these, for example: http://www.performancebike.com/shop/profile.cfm?SKU=2311&subcategory_ID=5430
For less than 20 bucks you're rolling.
http://www.performancebike.com/product_images/250/44-1656-NCL-TREAD.jpg
Here's a slightly skinnier one, for a few bucks more.
http://www.performancebike.com/shop/profile.cfm?SKU=2314&subcategory_ID=5430

I put Specialized Nimbus 26x1.5 on my full suspension. It added about 1.5 mph over the knobbies and gave a much better road ride and worked well on relatively good condition rails-to-trails.. However, it's still not nearly as comfortable as my Cross bike with drop bars for longer road rides, but it does give an improvement for minimum bucks.

Don't convert the bike, it will not react the way it was designed to. If you spend 300 on a used bike (hybrid) you will not regret your choice. I just picked up a used 05 trek 7300 on Craigslist, paid 150 for it, put a couple of $ into it, cleaned it up real well, what a great deal, I'm so happy with the choice I made. Hopr this helps

The Jamis Eureka is a mountain bike that has a design well suited for hucking and doing some biggerdrops and not a bike I'd consider being a good candidate for a hybridization.

Finding a used road bike that you can add flat or riser bars to or a decent used hybrid is the better way to go and could cost you very little...

I picked up a '99 Trek 7500 for a little more than $100.00 last year (mostly for the frame and wheels) and have taken this hybrid and been converting it into a heavy duty cross bike... I'm running 700:35 cross tyres (1.4 inch tread width) that are most capable on the road and very capable on the trails and singletrack.

Ok, I have decided to sell my Jamis Eureka on Craigs List. My price range is now in the range for a nice hybrid $400-675. I have looked at the 2008 Coda Sport, The Motobecane Cafe Noir, and the Bianchi Boardwalk or Strada, thanks for your help, any input would be appreciated. I am basically looking for a flat bar road bike, and I am not partial to Treks.

I like my Trek bikes (6700 and 7500) and when it comes to hybrids the Multitrack and FX series deliver some really good bang for the buck.

There's a good selection of hybrids out there and you might even consider looking at some cross bikes w/ flat bars since they are going to be a little zippier than a hybrid and who knows...you might even want to try riding drop bars.

My 7500...

http://members.shaw.ca/feynn/biking/7500mx.jpg