Hello,
I had the same probs and the solution for was NO ICS!!!
Somehow OFP doesn´t like the Internet Connection Sharing of win98SE and XP. The server of the network has no problems but the clients do.
Try using ´Sygate home/office network´ or ´Winroute lite/pro´ for instance.
But then again i don´t know if you are on a NAT but if you are try this!!
Greetz.