I would be really careful putting fabric in a laser printer. The laser printer fuses toner to paper and it can get VERY hot inside the printer. It could potentially ruin your fabric and your printer, so be careful.
I would recommend using an inkjet printer. You can either buy pretreated fabric or use bubble jet set, which is what I use. You just soak the fabric in the solution, let it dry flat, iron it to freezer paper and trim the edges. I should note though if you have an HP printer you should use the BubbleJet Set esp. for HP printers, you will be much happier with the colors.
Once you print your fabric (pretreated or treated yourself) you should let it sit for about 30 minutes to cure. Then rinse the fabric in hot water to get rid of excess ink, iron it and then your ready to sew!
Drew