...including defrag, cleanup, virus scans (clear), hijack this (clear)...

Basically computer can barely handle stuff like youtube, which is jerky. Most games are a nightmare. I use Firefox rather than IE, though the tabs often only respond after 30secs or so (and the address bar fails to update). Most of these problems occur after about half an hour of use. Any ideas? Much appreciated...

Windows XP, SP2
Motherboard:
CPU Type - Intel Celeron, 2800 MHz (28 x 100)
Motherboard Name - Foxconn 661M03-G (3 PCI, 1 AGP, 2 DDR DIMM, Audio, Video, LAN, IEEE-1394)
Motherboard Chipset - SiS 661FX
System Memory - 736 MB (PC3200 DDR SDRAM)
BIOS Type - Award (11/05/04)
Display:
Video Adapter SiS 661FX (32 MB)
3D Accelerator SiS 330 Mirage Integrated

I would say a you have a lot working against you; the Celeron, on-board graphics, and only 736Mb of RAM. On-board graphics, in general, is a huge bottle neck for any graphics intensive task, and yours is on the lower end of the scale at that. 1Gb of system RAM per CPU core is recommended for adequate performance and you only have 768Mb. 32Mb of that has been stolen and dedicated for graphics. Finally, Celerons are budget CPUs - no way around that. You have a good office machine. Not a game or graphics machine. You need to upgrade to a decent graphics card, toss the 256Mb RAM module and get another 512Mb RAM module, as a minimum. Then, even with the Celeron, you should get okay performance.

However, what you have now does not explain 30 second load times. How do you connect to the Internet? And what do you mean the address bar fails to update? You never see the page address in there?

How much free disk space do you have?

Besides scanning for viruses, what about spyware?

First, cheers v much for your help, I'll take your advice re the RAM & graphics card. Any one you can particularly recommend btw? You're right about the office machine - that was the flip side of getting a free computer...!

The other bits: It's not so much the connection that's the problem. I can usually use the keyboard tab to switch between the Firefox tabs and there's no delay, but it's when I use the mouse that I get the slow response times. And with the address bar, it won't register that I've switched between pages for a while (eg it'll still say bbc.co.uk when I'm on a tab on google, say). Then after a while it'll quickly catch up on itself and flash through all the pages I've been looking at. It doesn't stop me from actually reading pages though, so it's really only a problem if I want to bookmark a page or copy the address bar.

I've got at least 20gb of disk space free - it's partitioned but pretty evenly spread. And I've done various spyware checks and usually come up pretty clear...

I can't recommend a card without knowing your budget, but even knowing that, it is too hard to stay on top of current technology and offerings to know the best available for the money. Fortunately, Tom's Hardware Guide does that for us by putting out monthly "Best Video Cards for the Money" lists. Do remember that your motherboard supports the aging AGP technology (so skip the PCIe section). The prices are in $US, but you can still use the list, pick a card, then check £UK prices locally.

There are still some great AGP cards being produced, but the best can not compete with good PCIe cards, and as AGP motherboards fade into history, so will AGP cards. If you expect to upgrade your motherboard in the next couple years, keep in mind you will not be able to carry the AGP card over to the new motherboard.

As to your address bar problem, I don't use FF so I am not too familiar with it. I found one reference to "address not updating" after upgrading to FF 2.0that suggested to check your extensions for tab related extensions like TMP (tab mix plus) and TBP (tab browser preferences). If you have such an extension, disable it. However, the same reference said updates were due out in the next couple days, but that was last October.

Another suggested the problem was caused by the Skype Web Toolbar - if that applies, upgrade to the latest version, but if the problem persists, uninstall the toolbar.

I have a canned text for cleaning systems of malware I can post if you are not certain your arsenal is complete.