This sounds like the position: relative bug in IE6/7
(RadMenu uses position: relative to ensure its submenu positions). The solution is to set position: relative to all your scrolling containers.
All the best,
the Telerik team
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Public Issue Tracking
system and vote to affect the priority of the items