Typically while still in school your loans will be in deferment. Mortgage lenders know you'll need to start paying on these at some point, so they have to calculate a monthly payment amount. This monthly payment amount is combined with your other debts (CC payments, car payment, etc) to calculate your debt to income ratio (DTI, monthly debt payments / gross monthly income). DTI is what they use to determine how much they'll let you borrow for a house. It will depend on what type of loan you go for (conventional, FHA, VA) but a common way they calculate monthly payment for loans in deferment is 1% of the total loan balance. So if you have $20k of student loans they will estimate a $200 monthly student loan payment.
To really determine if the student loans will affect your ability to buy a home we'll need some additional info. Your income, current debts/payments, what price home you are shopping for, how much you expect to borrow in student loans.
