Install XP over OEM XP

[Lynne]

There seem to be features that are not available to me because I have the
OEM version of XP (backup and, a true Windows XP help system - I have Help,
but it's Compaq's version, not XP and it's not all that great. And, should
something happen, it makes me "nervous" to not have anything other than
mfgr's "Restore" program and restoration CDs that I burned. Can I simply buy
a copy of XP and install it over the existing OEM, or, would I have to
reformat, clean install?

Thanks.
Lynne