Hi Rans6
The advice on MSCONFIG is good. The reason I use Hijackthis is that it shows some important stuff that starts automatically that MSCONFIG doesn't.
To interpret the log generated is down to experience. Run HJT, view the log and google for anything you don't recognise. You soon learn what's "normal" and what warrants further examination. Feel free to post the result here for a health check but please do read it first as some entries can be embarassing and/or a security risk.
I would also concur with the RAM boost advice. Topping up the RAM is usually the best speed boost you can give a machine if you're not doing heavyweight graphics stuff.
A good(ish) rule of thumb for a pagefile size is 1.5 times RAM so in your case, around 760 Mb. Another speed helper is to set a custom size for it and set minimum and maximum to the same size. This stops Windows from resizing it which can help performance by reducing some fairly intensive disk operations and also reducing disk deframentation. If you have 2 hard disks, set a page file on each one. If you have multiple partitions on a single disk, put the pagefile in the same partition as Windows - swapping partitions is a relatively expensive exercise and with a minimum amount of RAM, as you have, will certainly slow things down.
In your shoes, I would try (in ascending order of ease/cost/payback)
1. Set the page file as above.
2. Defrag the disk(s)
3. Run ccleaner to clear out the rubbish. Caution, if you choose to delete cookies, make sure you know your passwords etc
4. Try a system restore back to a point where you know it ran OK
5. Try the One Off Browser. Firefox can be a resource hog similar to IE and both are fairly crappy. TOOB has a lot of shortcomings but is extremely resource friendly. This would help to eliminate IE8 from the mix
6. Add RAM. Mad_jock is right, if the mobo will take it, put 2gb in, not much point going to 1 gb altough it will make a big difference either way
Hope this helps...
Cheers