Using audacity as an amp with no latency

I am using audacity 2.0.2 , I have win vista 64 on a hp laptop with 4 meg of ram and a 2.27ghz processor.
I am trying to play my guitar (plugged into the external mike input) thru audacity using it as an amp (with recording paused)
while playing audio from music files on my laptop.
I can not get the latency issue resolved to be able to play in real time.I tried to set the latency settings in the options but can not figure it out.
Please help ,or tell me what software I might use if audacity won’t do it.

The one word version is no.

There are two latencies. Recording Latency is the one we can fix. That’s the one where you sing in perfect time to your backing track and you adjust Audacity so your voice comes out in perfect time when you play it all back.

Machine Latency is what your headphones get when you play an instrument in real time. You’re stuck with that one. We can’t change the size of your computer. You can use one of the hardware solutions we reviewed like the UCA202.®_UCA202_Stereo_bidirectional_USB_Sound_Card

You get your live foldback and theatrical mix from the external sound card, not the computer.

You can solve this latency in Audacity by recompiling the program with ASIO software. That’s basically creating a new Audacity program with new software.

Or you can pop for one of the money-based software products that use ASIO software internally.

Or you can just put up with not being able to hear the live mix.