Originally Posted by T-Mar

As previously mentioned, all bearings can be replaced if they are worn out. The question is the expense. Worn out hub bearings are worst, as you either have to go through the expense of re-lacing the rims on new hubs or buying new wheels. A new headset, pedals, bottom bracket or freewheel are not verly large expenses, provided you do the work yourself and they do not all need replacing at the same time.

Overall, in the long run, I think it benefits to learn bicycle mechnanics and invest in tools. A co-op is great learning experience. If you don't have one, there are many great on-line sources but I prefer books, as I like having the instructions in front of me while I work. Most used book shops have a wide variety of repair manuals available at reasonable prices.

As for the pedals, sometimes the thread are marked on wrench flats. If not, remove the pedal and compare the threaded end to the one from your wife's bicycle. A 1/16" difference in diameter wil be readily noticable, if you have the smaller size.