I'll concede limited defeat on the 1%/6%/10% thing, because one person's idle is another person's quite busy what with Skype, VPN, encryption drivers and stuff doing their thing.
And the machine's been defragged. And we can assume the swap area is fine, and there's enough RAM since the computer has slowed down, not always been slow. So I concur, it's a quest for the pile of stuff starting up at boot time.
I'd be tempted to try a safe boot (F8) and see if that feels a little faster, then that would point one in the right direction. I'd normally recommend running Hijack This, but the listing tells strangers an awful lot about what one does with one's computer and it does seem to concern people around here
. Would be nice to know if there's anything sat there thinking it's a server of some kind, though.