Windows New Vegas Resolution

[China cat]

I'm trying to play Fallout New Vegas after I used Bootcamp, when I try to change the resolution to 1920x1080 from the menu nothing changes. No matter what resolution I choose it doesn't have any effect. I was going to change the isize in falloutpres but it's already set to 1920x1080. Does anyone have a solution that might fix this?

 

[Washac]

I think people will need to know what model your Mac is, which graphics card you have, how much memory you have, which version of windows you are running, and I assume this is the Steam digital download ?

 

[China cat]

Oh right, sorry

I have mid 2011 21.5" iMac
I'm running Windows 7 Home Premium
Graphics is - AMD Radeon HD 6750M 512 MB
I have 4 GB of memory, and yes it's a Steam digital download.