Wal-mart is pretty vague about what kind of file it is, though they claim you can play it repeatedly.
As for the size, here's the info:
Available Movie FormatsWith all sorts of companies (from Netflix to iTunes to Wal-mart just to name a few) competing in the digital download space, the competition should be quite beneficial to us consumers!
PC Format: Recommended for our customers that do not own or intend to purchase a compatible portable video player. PC/Laptop videos can be played on a PC/Laptop or on the TV via a Windows Media Extender (e.g. Xbox 360) or through direct connection from a PC to a TV. Videos in this format have the highest image quality. Technical Specification: 640 X 480 maximum resolution, 30 fps, 1,500-1,700 kbps average bit rate. THIS FORMAT WILL NOT PLAY ON MOST PORTABLE VIDEO PLAYERS.
PC & Portable: Recommended for our customers that own or intend to purchase a compatible portable video player. This bundle provides the greatest flexibility providing you two files: one to play your on PC, and one for your portable players. This bundle requires approximately 30% more storage space and time to download as a stand-alone PC/Laptop format. PORTABLE BUNDLE FILES ARE NOT COMPATIBLE WITH iPODS.
Available TV Episode Formats:
Portable Format: Our TV episodes are optimized for fast downloads and viewing on the go. All TV shows can be played on both your PC/Laptop and compatible portable video players. Technical Specification: 320 X 240 maximum resolution, 30 fps, 500-810 kbps average bit rate. PORTABLE FILES ARE NOT COMPATIBLE WITH iPODS.