I use Windows 7 Home Premium as the OS in the various virtual machines I run. This is a space saving thing more than anything: I've limited the boot drive space to 20GB on my base VM so that I can have as many cloned VMs as I want on my external drive, and I'm assuming that Ultimate takes up a lot more room. Anyway...
The base install of Win7 Home Premium sets passwords to expire after 42 days. For a VM this is somewhat overkill (after all, I have to log in to my real machine in order to run the VM), so, today when I tried to log in and the OS came up with "your password has expired, change it" I decided to fix it instead.
Unfortunately the standard way of fixing this (running lusrmgr.msc -- just enter that in the Start search box) doesn't work in the Home Premium version because the snap-in it runs isn't present. Bah. Instead you have open up a Command Prompt as administrator (type "Command Prompt" in the Start search box and instead of just pressing Enter as normal, you right-click the menu item for it and select "Run as administrator") and type the following command at the prompt:
net accounts /maxpwage:unlimited
and press Enter. That should do it. (If you get access error 5, you didn't run Command Prompt as administrator.)