I've been asked by a few different people about my spreadsheet, so I'll post a link to a few different ones.

The first is a set up with 12 females and 2 males: 1 litter a week. Props to Lord Jackel for making it blatently obvious to me.
http://www.geocities.com/cloudlessgrey/12female.xls

And the second is my spreadsheet, using 10 girls, 2 males: 1 litter a week.
I've split this one in half for me to use right now, as I will be raising 4 females from my first litters, so i'm actually getting a litter every 2 weeks.
http://www.geocities.com/cloudlessgrey/10female.xls

It should automatically download and open in Excel when you click on the link.
If it doesn't work, ummm... I may just have to email it to you. Just PM me.