OK for a 'quick answer'....
One thing to think about is if you run any anti-spyware software (Spyware Doctor, Adaware, SpySweeper etc.) - it may be that this was 'extending' the functionality of the popup stopper inbuilt in IE6 (because it surprises me you found this worked - it was pretty pants imho); and these apps may not plug-in to IE7 properly yet.
The other thing I'd note is that MS are still putting out bugfixes and security updates for IE; and it's been in the wild for YEARS. IE7 is still VERY new, and as such, I wouldn't expect it to work properly for a while yet.
I guess we could probably pinpoint something closer to the cause of your problems, maybe get fewer popups and a slight increase in performance for your system (btw, performance will drop because internet explorer is a pretty integral part of the windows experience now, so even when you think it's not running, it is (or components of it), and IE7 is just bigger and heavier than IE6 so this probably explains the slow-down effect you've found)... But if I'm honest I'd say the quickest and safest way to get system performance back and minimise the popups and spyware you're subjected to while retaining most of the IE7 browsing improvements is to...
Uninstall IE7 and go get FireFox 1.6 (or if you really want to be up-to-the-minute, 2.0 (but like IE7 this still needs a bit of work, albeit nowhere near as much))...
It's a lot lighter on system resources because it isn't sewn-in to everything else that's on your PC. It's a lot more popup/spyware proof a) because of the way it's written and b) because most malware-writers are too lazy to write code that will trash Firefox as well as IE, so they just hit the masses using IE. and c) most of the browsing enhancements found in IE7 are Microsoft spins on ideas that have been in Firefox for a long time. ...Plus there are thousands of free plug-ins for Firefox that make it even cooler.
Now don't get me wrong, this isn't me just going MS-bashing for the hell of it (*smiles at any MS reps he works with who may be reading this*); but it is simply that I think looking at their past record on software rollouts this would probably be the quickest and easiest way for you to get your problems sorted out; I just can't help thinking you'll be waiting for a month or two for updates to IE7 (or indeed, service pack 1) and maybe the anti-spyware apps which need to interface with it...
Regards,
Rob.
