iPhone Memory Problem?

I have an jailbroken iPhone 3GS 16GB and had some issues when trying to sync large sized apps (Gameloft games mostly) Like the new Driver game that came out for example, I just can't seem to put it on my phone. The game is 405MB, and the first time it told me I didn't have enough memory on my phone it was displayed in iTunes that I had 600MB free. I started deleting some stuff off my phone and managed to get it up to 900MB. But I still can't put this game on my phone. It also says when I go to settings on my phone that I have 900MB available. Is it just a display error, cause this is really confusing the hell out of me. I had the same problem with Modern Combat, I had to free up 600MB to put a 200MB game on my phone, should I just keep deleting stuff or is there something I can do so it can actually tell me how much memory I have? I know Cydia has one of those things that tells me how much memory I have, but it's not working atm... not that that would probably help.