Yeah, as jbennet said...IE7, or rather Windows, for that matter, doesn't like running a lot of stuff with less than 512MB installed. Now, technically you DO have that much, but 480MB is an odd number, which means you have onboard video. Either you have a non-gaming desktop or a laptop. Either way, I'd suggest a memory upgrade first.
Also, do you run multiple windows of IE7, or are you using tabs?
As a suggestion, after a fresh reboot and without opening IE7, open the Internet Options window (on desktop or Start menu right-click IE7 icon or open it from the Control Panel). Empty Temporary Internet Files and Cookies. Might empty history as well to be safe. Once finished, click on "Settings". You may get a message about there having been too much space used or somesuch. Just click OK. When the window comes up, if the number for the Temp. Int. Files is bigger than 250MB, I'd drop it back. I generally use 128MB, but I've seen as little as 50MB work just fine.
Next, click View Objects. Anything that says "Damaged", get rid of. Just right-click it and Remove. You might get minor warnings about it not completely getting rid of it, but just click OK. Also, if you have a LOT of them, look through them. You should be able to open them up and see what website it came from towards the bottom. If the website isn't familiar to you, or the control seems suspicious, just get rid of it. These aren't mandatory files and can be removed without crashing the system. Worst case, they just ask to reinstall themselves when you re-visit the website.
Once that's all set, make sure you hit Apply, then OK. (OK applies anyway, but why chance it?) Do this until all the config windows are closed.
Reboot just to give it a fresh start, and try again.
I'd still upgrade the memory, regardless, but the cleanup should at least help. Let me know how it works.