im totally new at this, lets say i partition my 1tb hard drive into /c and /d . /c will have my windows 7 ultimate on it and /d will have everything else.
when i install stuff should i install on /c or /d or am i force to install something like anti virus on /c?
will installing/ having all my files on /d and leaving my /c clean with os on it only improve performance?
I would install programs into the same partition as Windows. I say this because when you start up a program it also needs to load Windows DLLs and having the two in the same partition places them closer together, minimizes head movement and improves startup time. (Note that the opposite would be true if we were talking two separate disk drives since I/Os could be issued to both drives in parallel).
And in Windows you can't move from one system to another without reinstalling all the programs anyway, so there really isn't any advantage to having them on a different drive.
IMHO it's worth putting the OS into it's own partition - this is mostly for ease of maintenance. You can back up individual data files, but the OS itself really needs to be backed up as a whole. By putting the OS into it's own partition (or on it's own drive) you can do an image backup of it without having to also include all your data files. Then you can use much smaller file-based incremental backups for your data files.
Having your data files on a separate drive can also come very handy when it comes time to migrate to a new operating system.
The backup program that comes as part of Windows 7 includes a "System Image Backup" option via a link in the upper-left corner of its main window. You'd typically make a system backup to an external hard drive.
If your OS disk dies, then there's no way to boot your system in order to restore the backup. To deal with this, the Windows 7 backup program also lets you create a "recovery DVD" - you'd burn one of these when you make your first backup so that if your OS disk dies then you can boot from the DVD and use it to restore your OS from the external drive holding the backup to the replacement drive.
In terms of the size that you need - I'd start with around 60-80GB. If you use a lot of games or other programs (or if they're very large), then add to that as necessary. You should be able to check the game's packaging or the web site you got it from to see how much space it takes.