I have an 8 year old G3 Wallstreet running at 233Mhz that can un-officially run Tiger so I hear. I've got Panther running on it. It is slow but works properly. A memory boost to 512MB would certainly help, since I only have 256MB in it right now. Is this a viable machine. Well for e-mail and web browsing it is fine. I did video editing on it when I had a 466Mhz card in it, but that doesn't work any longer. It would be OK for Cocoa programming and non-professionaly image editing, and using MS Office. Using anything that challenges the graphics system would likely be unadvisable.
Considering Microsoft hasn't released a new version of their OS in 5 years, I'm not sure why you'd be seeing the problems you describe. I have heard slow downs can occur due to software problems, but out right freezing seems weird. Defragging your hard drives may help with some slow down issues.