Well, that gets the basics out of the way.
Despite the dire warning about handling the swap file settings yourself, there is really no problem to it and you can always revert if you experience a degradation in performance (unlikely)
Most of my machines have been set manually or killed completely and allowed to run in physical memory only. Never a problem with it.
The reason for the defrag following the cleanout was in order to get the swapfile all in one block on the hard drive to stop it interfering with your other material there. If it is all in one contiguous block it is more efficient.
It is even better on an internal slave drive but as you don’t have that you say you don’t have that option and certainly putting it on an external drive would hardly seem to be a wise move.
Have you tried the Spybot Search & Destroy advanced mode tools?
The Secure Shredder will find and dump stuff that XP doesn’t know about.
The Startup list will find stuff that msconfig isn’t aware of. It will in most cases give a description and advice on whether it is an essential function or superfluous.
The Hosts file is similar to the Immunize function in blocking known bad sites.
System internals will fix any tangled up mess in the registry.
Despite the warnings I have run all those functions and all the remaining ones - mainly to see how much havoc they could wreak, and never had the slightest problem.
You don’t list a specific AV program.
If you don’t have it, may I recommend Avast.
It will after installation ask to run a boot-time scan and if permitted will scan and fix/archive anything it finds with Windows inactive. Less chance of the slippery little buggers evading it!
A note of caution though. You MUST stay with the machine during the boot scan and keep shoving the mouse around. If the machine goes into power saving or hibernation the effects are dire - I had to reinstall Vista - found out the hard way.
I’ve used it on several machines since and not had any problems once that is observed.
You will be aware of the ‘Hijack This’ option. and have presumably considered this.
Have you used CWSShredder?
Although SS&D will find and remove some of them, this is worth running now and then. Click the ‘stand alone version’ link or they will ask for cash.
Coolwebsearch doesn’t JUST redirect your browser pages, there are other little bits of nastiness associated with it.
A lot of people have cited the Firefox memory leak as a problem and as you say you don’t use it by default. I have never encountered a problem with it but it would not appear to be the reason for the slow down.
Have you installed anything recently that could be taking up resources? Any updates? There were some updates from Microsoft a few weeks ago that were reported as giving a slew of random problems including slowing systems down.