After a little searching around, I was able to find some photos of a party back in December that supposedly launched the store. There you'll see some photos of designs that aren't (yet) on the store site. Longer term, it sounds like Microsoft plans to make this clothing available at brick-and-mortar stores; maybe they are there already, but I can't tell because none of the stores are near me.
I don't understand the target audience of this clothing line. The products themselves evoke memories of mid-1980s Microsoft that probably can't be recalled by anyone younger than 40. Yet they're being sold by Urban Outfitters with some sort of hip-hop connection? Yeah, the hip-hop crowd fondly remembers MS-DOS and the launch of Microsoft Word in 1985. Maybe the T-shirt with the mug shot of Bill Gates will sell well. The poor guy hasn't been gone from the company for a year and they're already making fun of his youthful indiscretions!
Although I initially had my doubts about this site, the prices finally convinced me this was real. The Gates mugshot T-shirt doesn't look very nice, but it has a beefy $24 price ($30 with shipping).