Your best bet is to get the grommets first The ones I use fit a 7/8" hole. I also use grommets for 1 and 1 1/4" holes for the IDE and 24 pin mobo.
If you go to Lowes you can get grommets. They are expensive but make for a nice look and help prevent chafing.
Did you have any pics with your mobo and all the other gear mounted?