Mac and Windows computers can't see each other on the same network?

I'm trying to set up a media server using an old hp laptop running windows vista. the computer itself works fine and can connect to the internet and see the other windows computers on the network, but my macbook pro running osx lion cannot see the hp laptop, and the hp laptop cannot see my macbook pro. i have file sharing enabled on both the mac and the pc, and i have smb sharing enabled on my mac, so i'm not sure what's going on. my mac can see the other windows computers on the network as well, it just can't see the particular hp laptop that i am trying to connect to. some assistance and a detailed explanation would be very much appreciated. thanks in advance