Unattend Installation

hi,

we did and upgrade form windows nt 4 to W2k active directory.
now we are planning to upgrade the clients to windows xp. using unattend installation, the problem is all the clients are using fixed Ip that required to run some application so how to keep the current ip after the upgrade I tried many ways but didnt work we need to upgrade the clients and keeping the same IP using unattend installation

thanks