Update as of 29th July 2012:
Bought two OCZ Agility 60GB SSDs (these -
OCZ Agility (AGT3-25SAT3-60G) 60 GB | CheckoutSpy.co.uk).
I had heard mixed reviews about the firmware (as said above) but not had a single problem. Installed like a normal disk, mirrored the drives (most complicated bit) and fired the two (Vista and XP) machines up. As expected, the machines are much quicker and will probably last us a couple more years. I will probably clean them both down too and reinstall the OS to see if there are further gains to be had there (perhaps a future update).
Highly recommended, especially if keeping the old HDs as backup/extra storage (not that these machines had much anyway!). I can't say how much quicker they are - certainly twice as fast booting - but they've removed sluggish applications completely. On one machine Outlook had always taken an age to load, largely due to the number of emails in the PST, but now it opens like notepad would.
Certainly feeling much SSD love - just thinking about upgrading my laptop now!