Hi Maz,
You definitely needed the memory but there are a couple of things you could do to speed things up and get back disk space for free.
1. Install a program called "ccleaner" and run it. You will probably want to check all the options under "windows" and "applications" under the cleaner tab. I recently did this for a friend and got back 5GB of space on a 20GB hard drive!
2. In ccleaner go to the "tools" tab and under start-up, disable (not delete) anything you aren't sure of - the only thing that runs for me is the anti-virus program, NOTHING else is needed. then restart. If something you use doesn't run then go back and turn the item on. So many programs install crap that runs and takes resources (mainly memory) when you don't need it e.g. adobe updater, lots of stuff in itunes, realplayer, some driver updates etc.
3. Give it a damn good defrag using the microsoft tool under system tools or a freebie such as that from auslogics. Repeat until you can't defrag any further and then get into the habit of running it once a week.
4. again in ccleaner under registery, do a scan and clean-up. I've removed over 20,000 bogus entries from a machine before.
This is what I do for friends of mine, most can quite happily use a computer for all their everyday tasks from 5-6 years ago. If I didn't do a fair bit of video encoding, I wouldn't have bought a new one since my previous 2.0GHz Pentium 4.