Hi,
Applied win2k sp3 and as2000 sp4 a couple of weekends ago. Did sp3 first on 4 servers and after the usual complaining about dhcp dns etc things settled down fine.
Then applied sp4 to all 4 servers plus sp4 for exch option. Everything went remarkably well, no complaints about it at all.
After a couple of backup jobs, 2 of the jobs kept hanging on .cat files in the arcserve temp dir. I applied the latest patch from CA and removed the temp dir from the backup job and that seemed to cure it.
One thing I have notice since sp4 or it could be win2k sp3 causing it - some files in the winnt\sys32 dir give errors saying sharing violation in the backup.
I have looked at the files and they are not really important so I live with it. It doesn't stop the backup job when it can't back them up, it just say incomplete in the job status.
I say go for it! What could possibly go wrong? (as the pilot of the Hindenberg said)