NIC (Network Interface Card) or just a network card. To back up data between a PC and for example another PC or Laptop. They are very cheap (about a tenner), easy to install, and will allow you to transfer data from one PC to another, in effect you would use tyhe second PCs Hard Disk as a backup device. Both PCs require a card and a crossover cable to link them. Other solutions could be a DVD RW (many modern drives now support all the formats available and will also do CDRW) the data which can be stored is way in excess of the 900MB files you specify.
Also, tape drives, separate Hard drives (LaCie do a good range), the list is endless. Or you can compress the data and stuff it on a humble CDRW, XP has compression tools but Winzip will also compress the data providing that it is not already a precompressed format.
ouch - thats quite a bit of transfering. Either of them have Network cards? if so just plug a lead between them and transfer at 100mbps. Regarding Zipping in my experience I would stear clear of compressing multimedia stuff like that. has a habit of corrupting the files and the amount of time taken to zip the files vs the amount of compression I would just (if you can) transfer the files the way I sugested