I run IE7 on XP and experience difficulties navigating between websites?

IE7 fires up ok and the initial 'window' works fine. However, if I try to
open a second 'window' (would normally come up blank) within the same IE7
session, the whole session locks up with 'Not responding'.

Closing and starting up IE7 works fine - same if I stick to only one
'window' per session. Seems to be the same with website links - works fine
when a new IE7 session is automatically started but not when it's the second
'window' within a session.

Tried de/re-installing IE7 (to IE6) - no difference? No specific evidence of
a virus?

I'm trying not to tie the start of these symptoms with Safari, which I
installed and then removed around the same time?

Any suggestions?