1) Make sure you know EXACTLY how big your vista and XP partitions are. Preferably in Megabytes.
2) Go here
3) Burn that file onto a dvd or cd.
4) reboot your computer, and press the key to go into BIOS settings. (usually it tells you what to press around when the manufacturer's logo come up. It's often F7)
5) Change the Boot Sequence (or similar) to CD first.
6)reboot again, with the disc in your drive.
7) GParted will now show your different partitions, but they're not named. This is why you needed to know the sizes.
8) it's a simple right-click, click and drag, etc. interface from here on in, and you can make your Vista partition take up the whole drive. (Leave any small partitions or your computer may not boot, sorry if you know this, but just being safe)
Or you could just stick either your Vista disc or XP disc in the drive, shut down, restart your computer ensuring that your CD drive is primary boot device, let the disc boot and then from their just delete the partition that XP is stored on.
Once done you can reboot in to Vista and use the device manager to reformat the deleted partition into blank free space.
Is there any way to at least remove XP from the boot manager? There's still 9 gigs of space on the partition being used which sucks but I can live with it as long as I can get rid of the 20 sec boot manager.
If you leave the boot manager alone which version of Windows does it boot into, if it's Vista then you need to go in to
Control Panel
System
Select the 'Advanced Tab'
Select 'Start Up and Recovery'
Find the option that says something like
'Time to display list of Operating Systems' and then set the figure to 0 or uncheck the tick box.
To delete the menu totally and prevent access to XP totally then select the 'edit' button
The primary boot OS should the first option and should look something like this
multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="XXCLONE: (Cloned Volume) [d:0,p:1] \WINDOWS" /fastdetect /NoExecute=OptIn
The XP OS will have different disk and partition values, you would have to delete that one however I would strongly suggest posting the contents of the file here first so that we can see what options you have since deleting the wrong one will prevent you from booting your computer.