Pocket Streets has been dropped as a product. It has never been intended for anything other than simple map viewing. The intention seems to have been for walking around in a dense city -- hence, no routes. The program was written for the Pocket PCs of 2000, before such things as SD cards, hence the size limit.
Occasionally Pocket Streets will come up on the microsoft.public.streets-trips newsgroup. The product is four years old, so don't expect too much. The people there will probably tell you about the same thing as I'm telling you here.
Basically, the PDA is going away. The Microsoft-recommended solution is undoubtedly to use Live Maps on a smartphone with a data plan. People without smartphones use dedicated devices. Laptop planning still has a nice niche, enough to support incremental annual revisions to S&T, but nothing major like what Office went through in 2007. Ah, well, sometimes you and I are much smarter than the market, which turns its back on good products!