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thanks for the answers. fo3nix/obonio: there's no one process really hogging the cpu.
the main problem was slow startup, it took several minutes before the pc became usable. problems seem to have got worse after a recent update of zonealarm. this correlates with what bob a job mentions.
one thing which has improved things somewhat is that i deactivated spyware guard. What with zone alarm being quite a complete program, i didnt think 2 progs continually running were necessary. since then, system seems better, will keep you up to date.
PS did a defrag only a week ago.