It appears to me that RAM is the big shortfall. Doubling it to 512 will make a huge difference. I don't know if it would make much more difference- or if it's possible- to increase it beyond that, as with the age of the machine other things start to become the limiting factor.
Everything that loads when the computer starts will continue to have a performance hit after the start process.
Any security applications should be enabled at start, anything else can usually be disabled. IM's won't be received, until the messenger program is subsequently opened. Links to AOL I'm not sure, it's the internet provider, don't know how that one works. From what I've read AOL are pretty notorious for running stuff that shouldn't be required, try disabling it and see.
Any other entries you aren't sure about, Google for a recommendation, or have a look at a tweak site, like BlackViper's, or PCPitstop. I've found both provide excellent information, particularly the former (tutorial and good explanations), the latter runs an Activex that performs automated diagnostics and tuneup advice. Takes about 5min.