from my experience having all the spyware, anti virus and adware crap does clog it up.

at the moment i run vista. i have AVG (full version), Ccleaner, Speccy (so i can monitor my system; temp, cpu etc) and recuva just in case.

I run FL9, Ableton and a hella lot of plugins, Toontrack and Tracktor DJ Studio. Not a single problem so far. Oh and she's hooked to the net all the time.

She has a Celeron 2.00ghz processor, 2gb of ram and its vista 32bit.