You can download the latest mIRC beta
here. Your existing license will be valid for mIRC 7.
Please note that Microsoft Agent is not required for mIRC 6.35 to function properly, despite what the warning dialog says. See Khaled's post
here.
The problem appears to be that Windows 7 assumes that any application that tries to load agent is a badly designed application that will crash if Agent is not present. So it reports this as a potential error, even for well designed applications that cleanly handle this situation.