OS is Windows Vista Home Basic.

When I try to set a recovery point it tells me that I need to remove data from the D: drive to make space. The system is set up to overwrite previous restore points but it doesn't work at all so I can't get it to record new restore points.

Anyone out there who can offer me advice on how to fix the system???

I accept that I am a newbie and that I may have screwed it up but would be very grateful to anyone who can sort me out.

(Moderator edit: moved topic to more appropriate forum. jgweed)

For starters I would private message a Mod to move this to the Vista forum as you posted this in the XP forum.

What is on the D: drive? Is it the recovery partition for your computer? If so, there's no need to make Restore Points there.
If it's not the recovery partition - what else is on it? What is the size of the drive and how much free space is left?

To turn off System Restore on the D: drive:
Go to Start and type in "sysdm.cpl" (without the quotes) and press Enter
Go to the System Protection tab
Turn off System Restore on the D: drive by unchecking that drive, then click on Apply and OK

FYI - the size of System Restore points will increase with activity on the drive - so even though it may overwrite the old point, the newer point may be significantly larger (so it may not fit on the drive).