Maintaining and manipulating your own yeast bank can be a very rewarding hobby. Anyway, be prepared to invest a conspicuous amount of time and resources to such an activity.
Although the subject is quite advanced, you don't need to be a veteran brewer to achieve good results, but some technical background and an understanding of the underlying principles obviously helps.
Thus before setting up your own yeast ranch, I strongly suggest you read some of the very fine books available on brewing science and techniques.
Don't be scared by the seemingly complex steps involved: the description might be wordy, but most manipulations are actually performed in a matter of seconds, and after some practice they will become second nature to you.
You will notice the stress on sterility throughout these pages. While a homebrewer can easily be satisfied with sanitizing his equipment, we will be manipulating very small amounts of yeast cells in a bacteria friendly environment.
Though very simple in essence, these procedures are performed by professional labs in sterile rooms or under laminar flow hoods.
Since we poor homebrewers generally don't have access to such facilities, we must settle for manipulations that can guarantee nothing more that a high probability of sterility.
Nevertheless, we really should concentrate our efforts, and strive for sterility.
The concepts and procedures I describe are the ones I use daily (well, almost. I do have a life, you know...), and are derived mostly from the works of G. Fix, P. Rajotte and information gathered on the internet (HBD and The Brewery), adapted to my own conditions and possibilities, and reviewed by professional biologists.
Special thanks to Joseph Kish for bringing to my attention the distilled water storage method.
Homebrewers are known to be an opinionated lot, and I'm sure each one of you will find ways to improve and adapt to his own taste.
This is in no way meant to be a reference, just a report of what I do. Apparently with a good degree of success, but as always, YMMV.