I drive very few miles, less than 50 miles per week. I am concerned that the nimh battery charge will drop too low. Is there a way I can use the 120 volt line from my home to charge the battery?
How many miles on the HV battery, and has the HV battery fan been cleaned before? Many prefer using the plug and play charger and discharger from http://hybridautomotive.com/ If you only need a top charger, this DIY thread may be helpful : DIY Grid Reconditioning Charger | PriusChat
Driving 50mi a week is just fine. It is about the TIME between the last on and the next on. If you drive 50mi in an hour, and then it sits idle for the other 167 hours, that's the worst case scenario but still not that bad. If you drive 2000mi in a few days and then it sits for 6 months, that's very bad. If you drive a mile a day up and down the road every single day, the car likes that too.
A glance at the battery level indicator on the MFD will tell you the level of the traction battery. With those years and miles, the grid charger mentioned by @SFO might be a good idea. Not as a means to keep the battery charged, but as a way to get the battery back in balance and probably extend its life. I don't think driving just 50 miles a week will hurt the traction battery. Depending on how many miles you drive per trip, you might be running down the 12V battery, through. That's simple to check with a multi meter to see if you need a 12V battery maintainer.