I have a Sun V120 with eri0 NIC set to 10-Half connected to Fa0/0 on a Cisco 2600 (Fa0/0 also set to 10-Half). I am seeing collisions on this link (as expectd with a 10-Half connection) BUT, what is an acceptable rate of collisions for this type of link?
FYI, the Sun box is showing 2983 collisions for 7363063 Input packets and 8012355 Output packets (About 0.04%) on eri0. The router is showing similar results.
If you want to get technical about it, half duplex on itself is not acceptable for a server.
I can't put a number to it, but if your backups are completing, your users don'rt have issues connecting, your web pages load quickly, are not experiencing latency, etc... then I guess your current level of collisions is 'acceptable".