I do not understand this thing of restarting and reassigning IP to same NIC. May be because I do not have experience with SHDSL.
However, are you trying linux and windows xp on same machine ?
And btw, instead of restarting winxp, try disabling the network connection and then change its IP to second set and enable it. Tell me if it works.
After this we can see how to make work it in linux.