Yes, you can but you have to install Windows 7 in another partition.
I suggest that you DON'T do this for certain reasons... for example: there are newer 3d chips.
That depends on what exactly you mean by that. You want to run Windows XP within Windows 7 you need to install Microsoft virtual machine. It's free. You want to replace Seven with XP, then you will...
what do u mean custom install? Give more details.. You want to upgrade to win 7 or just format the pc and then put them on.
To find out go apple website and click on the mac basics