I respectfully disagree with pdarg , as a cut in the area he suggested (2-3K as a first response) could take out all the presence in the vocal, unless you are using a mic with a big bump in that area, freq. response-wise and you need to compensate.
It is hard to give advice without hearing your track, but generally the first place you go to compensate for the "nasal sound" is EQ around 900-950. Try in that area first. If you don't have a good spectrum analyzer (actually, even if you do), vary the Q a bit and the dB until it sounds good to you. Then check with someone else to see if in the process of tuning, you have convinced yourself that it sounds good.
If nobody else is available to check your work, rip a great vocal track from someone else, play in through media player or something, and A/B with your current track (that you just EQ'd) to bring perspective.
Best,
Mark
Edited for clariy