thanks for the technique tips! i guess my problem was that i was pushing up on rather than sideways... it took me forever to get the tire stretched over the rim like that. now, i am going to have to start preparing for winter. should i:
a) buy new tires for my current rims for this bike [what would be the max width on the tires i could safely install? and would that width work well in snow?]
b) buy new (wider) wheels and wider tires and just use them in the winter?
c) just buy a different bike for winter commuting [hybrid or mtb type]?

are all 700c standard widths? or are they made in different widths? how would i measure the width on my rim to figure out an appropriate max width for a tire? thanks a lot for all the help, and i apologize for all the [seemingly] silly and redundant questions.