How do I find my XP PC IP address from my Mac for RDC?

I am using RDC and it works fine. Only thing is my XP PC keeps changing it's address. I can not find out how I can find the PC's IP address, from my MAC, so I can use RDC. I did it the other day but forgot where I did it. I thought it was in Sys Pref>Networks but didn't see it and also did n't see it in my router.

Any ideas. Again, I know I did it. The other way is to go upstairs to the PC and do ipconfig but I am trying to avoid that.

Thanks!