It took some looking on google and a couple of assumptions. I am assuming by dynamic IP you are using a DHCP server, so a quick search on google for: XP DHCP release, about the fifth one:

http://www.its.uiowa.edu/cs/helpdesk...dows%202000/XP

Step by step instructions on how to renew and release DHCP assigned IP's. DHCP essentially works by having your server request an IP from the DHCP server. The DHCP server responds with an IP address (and at times, default gateway and sometimes even nameservice inf0). The DHCP server will then keep track that it has assigned that specific IP address to your server (a lease). The lease can either be permanant or temporary (times out eventuallY). Your computer (the client) can also tell the DHCP server that you are done using the address and that you no longer need it and it can give it to someone else (release lease) or conversely, you can tell the DHCP server that you still need an address and renew it. I suggest reading the article, but the skinny of it is:

ipconfig /release
ipconfig /renew

Hope that helps,

Neb