I dont see any connection between Peerguardian, metacafe, and avast.
Can you right click on desktop?
If yes, right click, arrange icons->show desktop icons. Check that option.
If not, for XP pro, start->run. type "gpedit.msc" without quotes, press enter.
under User Configuration->Administrative Templates->Desktop
see the state of "Hide and disable all items in desktop" if its enabled, double click it and choose disable, click ok and relog into your account.
for XP home,
start->run. type "regedit" and press enter.
browse to
HKEY_CURRENT_USER\Software\Microsoft\Windows\Curre ntVersion\Policies\
Explorer
or
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\Curr entVersion\Policies\
Explorer
depending on your problem exists only on your user account or in all user accounts.
You need to look for a DWORD value of name "NoDesktop"
if it exists, double click it, set the value as 0, and restart computer.
if it doesnt, right click on the right pane, new->dword value type the name as "NoDesktop" and double click it, change value to 0 and restart comp.
that should do it.
<phew>