both linux and ms could be very stable depending on how well you maintain the machine. it would really depends on the operator to install necessary program versus testing. if you're going to test apps and so forth you should really have another test box or use something like vmware to create test guest OS and apps. if you start playing around and creating your own kernel in linux, less you would need to "reformat" since you're only compiling core's only. lot of good documentation can be found at: http://www.tldp.org

i would also recommend finding a local linux user groups (lugs) in your area and get their opinion or attend one of the installfest to understand building linux from scratch. check out knoppix as well if you just want to learn how to use linux and not use your HDD.

-w0rm3y