I suggest you to upgrade to 2000-4-3a-sr2. I have been using this release for enough time to suggest it. So the version is oky.
Steps:
1- download win-OS-Upgrade-K9.2000-4-3a.exe and win-OS-Upgrade-K9.2000-4-3a-sr2.exe from CCO
2- First upgrade PUB to win-OS-Upgrade-K9.2000-4-3a.exe and then to win-OS-Upgrade-K9.2000-4-3a-sr2.exe
3- Secondly upgrade SUB to win-OS-Upgrade-K9.2000-4-3a.exe and then to win-OS-Upgrade-K9.2000-4-3a-sr2.exe
4- Multiple reboots will be required during the installtion, and each time you have to log in with admin account to continue the installation phases.
5- Before upgrade disable all antivirus "Mcafee etc." and all intrusion prevention "CSA etc." programs.
6- During the installation the callprocessing will be inturrupted.