Vacation software

Does anybody know of a program that plans vacation time off for employees. What I'm looking for is we have 90 employees some have 5 weeks off some 4 ect. only 7 employees can be off in the same week , so I'm looking for something that will block out a full week (7 employees of nobody can put their name in that week) also somthing in the program that wont let them bid weeks that the don't have comming ie john has three weeks to pick , so when his third week is picked he can no longer add to his weeks. Thanks in advance. Bob