Yeah, its the fact the computer has to stop processing the game, and bring the desktop back into focus again behind.
So yeah, everyones right here
It will still take some time with a gig of ram but will be a bit faster (we have a gig, and I've seen my brother minimizing it. Takes around 2 seconds to minimize, and about 5 seconds to maximize back) 512mb is rather alot though, and shouldn't be bothering you in any way while playing that much.
If you pause the game for example before minimizing (alt+tab), does this speed the process of doing it up?
I'd also think if it lagged online, it could be your internet connection since its a fully online game, and lags could be caused by that, if the game suddenly froze and when it comes back, players are in another place for example.
If it was more a jerk that carried on, it would be more the video card though I have the 9800 PRO and my brother can play the game at 1024x768 at high settings at about 30-40 fps (I guess thats okay) and would just be a case of lowering settings to a more suitable level if you wern't happy with the speed.