Go for it. I don't know who or what "BT" is, but AOL downloads a lot of "extras" you don't really need. Be sure to use a search engine to find out how to get all of the AOL off your computer. PS: Windows doesn't slow down as it ages, it slows down as you add more and more things to your start menu and files.
My home PC is Windows XP 5 years old in Jul 07. My ISP is AOL (because I knew no better at the time of getting a PC) I'm wondering has AOL got anything to do with slowing up my PC although I have heard XP slows as it ages. I am going to get rid of AOL and go to BT for my services and Broadband. AOL disconnects on a regular basis and just recently I have been using another browser which is brilliant - Firefox.