#1
How do you eliminate the lag in the Audacity when you record stuff.....its so annoying.
#2
If your sound card is stock, most likely, you can't.
One thing to do if you have already recored the backing track into Track 1, then just record yourself and play along with the song. After that, take your track 2, just highlight and cut out about half a second from the front to make the timing fit (its a little scissor icon).
Best is if you don't use computer recording for something like electric guitar, a computer stock sound card just can't handle it. If your really serious about recording yourself and producing your music. Get proper software ('Realistic' MIDI sounds, WAV/MIDI to MP3 converters and such) and a recording console, a good one should cost about 300 USD and an SM 57 (Dynamic mics can handle really loud noises) should cost about 70USD.

Good luck with all your recordings, hope this helped.

Thanks,
Royce Lee