That happened because when you did "urpmi kernel-source", urpmi took the latest available kernel source i.e. 2.6.3-8 from the "updates" source.
Your kernel 2.6.3-4 is the one distributed in the initial 10.0 Community edition.
At this point, you can either go for a kernel upgrade (see HERE
for instructions) to move your kernel to version 2.6.3-8 (this is what I did)
OR you can install kernel source 2.6.3-4 that should be on CD 3 of mdk 10.0CE.