XP & Vista loaded. Want to get rid of XP

[#1]

My wife`s laptop, has XP & Vista loaded.... I think she is getting XP automatic updates, as well as Vista updates, thus filling up the HDD.
Is is possible to remove XP without a complete re-install of Vista...
XP is listed on C:\ as  windows.old
Can I just delete this folder (and all files inside) and then run a registry cleaner, to clear out all the leftover registry entries?

[#2]

She will not get XP updates unless she actually runs XP.

[#3]

I still want to remove XP to free up disc space on the HDD.......

[#4]

In the Control Panel, under "Programs" is there a "Windows XP" listed?
Hopefully yes (if you performed an XP->Vista upgrade) which should give you the option to Roll-back to XP, or remove the XP installation.
Obviously, you want to remove the XP installation!
B.

[#5]

Will have to have a look, but don`t think so.....
She loaned her laptop to a chinese student so he could log on to his home blog, and somehow managed to install a virus, which eventually crashed the vista that was on it....
I put XP on as a temp measure.
Later, put Vista back on, so now I get the option to boot either when booting up. Vista is the "preferred" boot option.
for info
Local disc C:\
Used space        32.9gb
Free space        35.4gb
Capacity            68.4gb
Local disc D:\     
Used space        1.44gb
Free space          4.06gb
Capacity              6.05gb