The old machine I was running was a Compaq, with 192 mb SDRam, and was rated at 533 Mhz. Pretty sure it was a PII. I could run some plugins, but say running three was pushing it. (three tracks, three plugins). Something like that. Having said this I also had a lot of other crap running on my machine, so it wasn't exactly optimized for audio. I could have pushed it a little further, but not a helluva lot.
My new computer has 512 mb DDRRAM, and is rated somewhere around 1.3Ghz. One of my crazy projects has about 20 tracks, half of them running effects. There is still a fair amount of room for more things. Plugins are most definately memory intensive, however.
One thing to do would be to record a track, add the neccesary plugins, then mix it down, and start over with that file. It'll then be viewed simply as a wave file, without plugins, therefor reducing memory load. Its a bitch, but about the only way around it that I know.
I know you said you cant afford a new machine, but in light of my new monster, its one of the best investments I have made. It really gives me the freedom to not worry about how much memory I have (to a certain degree), and lets me mess around with plugins while running n-track, without jumping and skipping and crashing.
Ok enough rambling

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