Hello April
I think you can do this - although, it's a bit of an issue as you have to know the relevant items to import. I've not tried in years !
If you go to ImportWizard, import from a text file, say NO to having the wizard help you. Then go down to the account | opportunity | product and map the fields there. This should do it - however, as it's based on the acc/opp I'm not sure it'll complain (personally, I always script them in myself).
Regards
Mike