Not many modern systems come with serial mice, expect us nerds that have old legacy stuff lying around and pull it out, because they just became useful again. Hey, why buy a new wireless keyboard mouse for your mediacenter, if you have some old IR integrated keyboard and mouse lying around.
However modern Xorg still supports serial mice, but alot of manual entry would be required, or try to use the new hald framework. It can be done by hinting it to hald via inputattach This example is for linux:
inputattach -bare /dev/ttyS0
If that works, put it in rc.local and remember to background it ('&')