1. get enough RAM... you've already done that.
2. buy a second hard drive. keep your applications on your original hard drive, and your audio on the 2nd hard drive.
3. defrag your application and audio drives.
4. turn off any background software, while you are working.
5. make sure that your audio card is not competing on the same IRQ as other cards... network/modem cards and audio cards are a big problem.
I have a 1.2ghz AMD desktop with 512mb SDRAM, a 20gb HD that i use for applications and a RAID-0 80gb HD (actually 2x40) that i use for audio data. I use the frontier design's WaveCenter card.
On the most plugin intensive song, I have 16 - 48khz/24bit audio tracks with Ultrafunk EQ and Compressor plugins in each track. I also have a DSP-FX delay plugin runnin on the guitar track. I then have 2 delay plugins, and a reverb plugin as aux effects. Finally, I have Waves C4 (multi-band compressor) and L1 (peak limiter) plugins in my main out.
I also have a 1.2ghz laptop with 512mb SDRAM, with a single 40gb HD, and the m-audio USB enabled Duo. So far I've been able to push 8 tracks of 48khz/16bit with basicly the same plugins mentioned above.
With a 1ghz system, you should be able to do quite well.