I'm having exactly the same problem, you can read my posts here on the forum, lot's people provided good tips and things to try, so far nothing has worked.
I spent 3 hours on the phone with Apple Tech Suport and talked to two different Experts, they couldn't help me and left at "sometimes Windows and Mac computers simply don't get along and/or they blamed it on my router, but it's a new dual bank linksys router, works great... except like you my mac can' see the pc's on the network unless I enter the info manually which is a hassle compared to windows were everything connects the moment you turn it on.
If you find a solution please let me know and I'll do the same.