How can I get in my LAN when I boot from a WinPE disk?

I have a home network of three computers, all under WinXP via modem NetComm
NB5Plus4. I have a few boot disks, including Acronis emergency disk. If I
boot a computer by this CD (from Acronis), I easily get in local area
network and can save backup (a disk image) of one computer to another, i.e.
through my network. It means that the operating system of this disk "sees"
neighbouring computers in my network.
But if I boot a computer by a WinPE disk, I cannot get in other computers of
my network. I can get in the Internet, but cannot get in neighbouring
computers.
Why? What and where should I change for this?
Thank you
Lev