One of our partners asked me yesterday - In Windows Mobile 2003 you had the slider bar to select how much memory was Program Memory and how much was Storage Memory... Can you do that in Windows Mobile 5.0?

Unfortunately you can't change it anymore. The reason you could in the past was that both the storage and the program memory were in RAM.  The slider was just partitioning the RAM between those two places.

Now they are in different physical media. Storage is in Flash ROM and Program Memory is in RAM. There's no good way to use ROM as RAM, so there's no longer a way to change the partitioning on the fly.