This would be an extemely difficult request to fulfill.  Imagine that the script reads any particular category structure and generates the various nested levels, using ASP string-handling techniques to truncate long names and replace the end with "...".  The deeper the levels, the narrower the button would have to be.  I think you would be better advised to design for a nice CSS treatment.

Additionally, there is the SEO question. I don't have any scientific evidence but after building sites for many years I am absolutely convinced that text navigation is indexed by spiders better than button navigation.  And since stores can be more difficult to rank than text sites, I don't think you want to do anything to make it tougher.