Here are some helpful resources related to heat press machines and t-shirt businesses.
T-shirt Forums – Most active discussion boards for t-shirts and anything related to printing garments.
T-Shirt Help Desk – A successful t-shirt business owner(Gary) showing you the tools of the trade.
T-shirt Riches – A informative site about starting your t-shirt business by Cartess Ross.
Custom Ink – T-shirt printing service and they let you upload your graphics with their web tool.