For road biking, nothing beats a pure roadbike... with some caveats of course. However, converting a MTB for road use can be done cost-effectively and you can still save up for a roadbike.
A CF seatpost will do very little. My suggestion would be a rigid Tange cro-mo fork for around $30 or a Kona Project 2 for around $45. Make sure you get one that's suspension corrected and roughly matches your current axle-to-crown. For tyres, I'd get some 1" slicks as others have suggested. You can usually find pretty decent ones for around $15 each. If you want a little bit of suspension for your butt, you might consider a saddle with a titanium rail. They can be had for as little as $75-$85. You might also want to get some bar-ends if you don't already have them. They'll help with hand positioning. Also check out Road-Ends from
Endless Innovations. They're sold out of the original but someone mentioned that their next generation version should be shipping soon.
Road-Ends
