Excel 2008 : Help with vacation accrual

This is a new system this year (2012) in our company for vacation: Our employees accrue vacation on their anniversary date based on tenure (7.5 hours up to 4 years, 11.25 hours up to 8 years, and 15 hours for all others). They accrue for only 10 months to get all available time; no vacation rolls over. Right now, all employees hired before December 31, 2011, have an anniversary date of January 1. All employees hired this year and moving forward have their hire date as an anniversary date. I have a spreadsheet that calculates accrued hours based on calculating the month we're in. However, I don't know how to account for no accrual in November and December. Neither do I know how to set up formulas for people whose anniversary is anything other than January 1. Can anyone help?