Its an XP configuration problem most likely.
XP by default doesn’t load networking until after startup has completed – this is what causes these delays. To fix it you have to enable “Always wait for the network at computer startup and logon” with Group Policy Editor on the local machine as this is only an XP policy object.
To fix it: Click Start>Run> type MMC> click File>Add/remove snap-in> click Add – select group policy object editor > Add > Finish > Close > OK.
go to Local Computer Policy > Computer Configuration > Windows Settings > Administrative Templates > Logon. Change the “Always wait for the network at computer startup and logon” to ENABLED. EXIT – you don’t have to save the console unless you plan on using it again.
This should fix your problems – also make sure the DHCP server is the default gateway on these pc’s.