Gotta start with simpler things first, no messing with registry or O/S. That's the last resort. My mom has an IBM XP laptop i bought her. When i do a simple
C Cleaner run every couple months it can free up gigs of crap! It has registry related things and and a bunch of other little utilities that may help. An app like that is great to run every couple days. What i do, got no issues for 4 years with my latest pc(knock on wood tho). Plus, i have Avast Home Edition and Komodo firewall. The point is i am learning to really stay on top of anything associated with being online in general. Crap gets in there big time and gotta clean it up all the time. That is my theory for increasing slowness.