Chessrock - Was that you who produced "Darth Vador's tribute to Led Zepplin"?

Man, and I thought William Shatner could sing!
eeldip - I agree with learning to get the most out of what you've got, just not to the point of ignoring the inhierant limitations of what you've got. Your "back to the subject" comment threw me a little. The equipment used is certainly part of the subject, wouldn't you say?
anywhither - Unless you're doing RAP, please don't sing like Darth Vador

. But the point Chessrock was making is to sing with your full voice. The first step in the recording chain is the source, and trying to make a weak vocal sound full is hard.
Ok, now let's, "ahem", get back to the subject. Here's the rub...
you've got a noisy, weak signal, and the things you need to do to make it fuller are going to make it noisier. The ultimate answer to this problem is to upgrade your equipment, but if that's a problem right now then you need to spend some time learning about gain staging and getting the best signal to noise ratio out of the gear that you have. Even with better gear, you still need to know this.
Gainstaging is about making every link in the signal chain do the work it's supposed to do - no more, no less. If one stage does too much, you get distortion. If it does too little, you get noise and poor bit resolution. You need the preamp to supply the soundcard with a clean AND hot signal, just ticking 0db, but never going over. Consider that one subject to study up on.
Now, the first and best tool to get a vocal to sit in the mix is the compressor, especially for less experienced vocalists. Back to the rub, while a compressor will bring up the weak parts of the vocal, it also brings up the noise with it. So a clean recording is even more important when you use one. You can put a hardware compressor between the preamp and soundcard, but it's better to record first, then add compression afterwards. Plugins are excellent for this. Again, this is a whole other subject to study.
Another very popular technique to use for thickening a vocal is to double track it. Sing the vocal once, then very carefully record a second track of it while listening to the first track, trying to exactly match the timing. Mix the second vocal much lower than the first and it will add a lot of dimension to the vocal.
Reverb is another widely used way to spread out a vocal and give it space, and of course you should work with the EQ. Very often the best results with an eq are obtained by cutting certain frequencies rather that boosting others. Most voices do well to have a little 1Khz cut and a little 5K boost, but experimentation is key.
Ok, I've gotta get back to work. Good luck, and stick with it.
RD