I have been with AOL Silver for over 10 years. My computer often runs slow and friends have told me that it's because the AOL software messes up my registry.
AOL isn't the problem. You need a spring clean. SmitFraudFix, CWShredder, AdAware, SpyBot, AVG rootkit cleaner, A decent Firewall that you can set to prevent IE from escaping, AOL provide a firewall but it is crap. It has its setting adjusted by AOL to their default.
And you want a decent AV I am not sure how good they all are but AVG works for me. Some Firewalls/AVs change your registry.
Stop registry changes with WinPatrol, SpywareGuard and SpyBot's Teatimer. You will be able to see any changes that are made when you have any of them. They will ask you if you want them.
SpywareBlaster is another good tool. But you probably know all this. When you use them in Safe mode they will find almost everything. If you find you have a lot of malware, run the set and reboot then get updates and start again.
If you are still running slow get HijackThis and post a report to a suitable forum set up to check them. There may be toolbars and stuff that need removing.
Run the programmes in the order listed. Some scanners have the annoying habit of claiming SmitFraudFix is a bug. You may have to keep downloading it every time you want to run it. Pity that.
That's what I use, my speeds are top notch. You can test your speeds on the tool available on this website. Click the Speedtest tab. Do it a few time and at different times of day.
I particularly like the anti-spyware scanner always running in the background. If AOL did affect the registry, it is very unlikely it would be a detriment to the service. How do your friends explain a registry change affects the modem?
Good luck.