SIP phone and Vonage

I am going to be setting up a home/office bit when I move in a few weeks. I have 3 home PCs on a 4 port router. For work I will be hooking up a 4th PC, a SIP phone (one of hose VoIP), and ordering a Vonage device for a line so I can have a dedicated modem line. One of my home PCs is my dedicated web and file server.
Am I looking at buying an 8 port router or are there other options?
Your ideas are appreciated.
If there is any other info you need, please let me know and I will post it in COMMENTS.
All PCs are XP SP2.