On the 5000 under PHONES, create a SIP PHONE. in SYSTEM/DEVICES AND FEATURE CODES/SIP PEERS/SIP PHONE GROUPS/<the group>/CONFIGURATION, set MAXIMUM NUMBER OF CALLS to 4.
At the phone, under SETTINGS/ADVANCED (default pass is "admin") set TIME AND DATE to use SNTP. under SYSTEM SETTINGS set server address...weird note: can't use leading zeros, so enter 10.10.10.50 (for example), not 010.010.010.050. Also enter the extension you created in 5000 as USERNAME, LOGIN NAME and PASSWORD.
That should do it. Should pick up everything else from DHCP (unless you need to enter manually)