Vista networking problems

I have 3 PC's at home. All 3 have a different IP addy assigned by my cable company. I pay extra for the additional IP's and I refuse to use a router. Please forget suggesting I use a router I perfer a switch.
I have 2 PC's that use XP Pro and one uses Vista Ultimate. My 2 XP machines share files and can see each other fine but I can not get my Vista PC to see them and share files.
Any help would be appricieted.