I'm going to write this assuming you're not a Windows guru...
Not that I am either, my specialty runs in systems a bit larger than that, like 10,000 Mips and more, and with 128GB of memory...
Too bad Civ won't run on them, it would be nice to have real memory exceeding the compiler's max virtual memory.
As far as I can tell, it downloads the savegame to your system, loads it up, and then communicates only changed data with all the peers. Things which affect the GUI are strictly local, other than ongoing unit movements, etc.
One potential network issue would be someone trying to join during the attempt at going to world view, since it does freeze the game dead in its tracks when someone joins. That would have to be awfully bad luck to continue seeing it more than once.
If you're on XP Pro, bring up task manager and add the columns for Memory Delta and PF Delta. This may work in XP Home too, I don't have it to verify that task manager works the same. Then get into the save and try to zoom to world view. While it's in that frozen state, jump back to task manager and look at the Civilization4.exe line, to see what the cpu%, mem delta, and pf delta are.
Chances are it's got a mem delta and/or pf delta which are through the roof. It is possible, though remote, that such activity would bog the system enough that the pitboss peer to peer thread doesn't get enough dispatching time.
Also if it's pf delta (paging activity) and your hard drive is doing a lot of seeking (relatively loud rattling noises), it might indicate a highly fragmented page file. The fix for that is pretty convoluted, like setting the max PF size much smaller, reboot, defrag, restore PF setting, reboot again.
