Do as Ratalovich says, check the workgroup name is the same as on the other PCs but also make sure the computer name is unique on your network. You'll probably have to restart at this point.
NB - XP defaults to 'WORKGROUP' here but 'MSHOME' in the Network wizard!
Then, connect to the internet and leave it open.
Run the network wizard on the 'new' PC only ensuring the workgroup is the same on all PCs (you indicate it's going to be MSHOME). There should be no need to run the wizard on the other PCs or use a setup disk. Just refresh 'my network places' and all should be fine.
If it's not, check your router hasn't blocked the new pc.