An application like the free
FileZ would allow you to see what's on your card, as well as the Treo. Given that, you could beam small files between devices but your best bet (if you're talking about a PC) might be to transfer directly from your card to the PC, using a card reader. If it's your own PC, you might want to look into
CardExport II, which will allow a PC to see your Treo's card like an additional drive.