The removal of restore points in ME and XP's System Restore is limited. You can't pick and choose.
You can delete all of them, by turning off System Restore altogether (this will get rid of all restore points including any trojan or virus saved in System Restore).
Another is to delete all but the last restore point.
A third method is to reduce the amount of disk space reserved for System Restore. When the disk space is reduced, the older restore points which are over the storage limit will be deleted.
All these can be accessed I think by right clicking My Computer, Properties, System Restore tab.
If you need to restore other files on your computer to a restore point which happens also to contain a Trojan (so that you can't afford to remove the restore point), you can try disconnecting yourself from your internet connection, disable your AV and firewall, then restore your computer to the "infected" restore point.
Once the computer is restored to the infected state, turn off System Restore (which will delete all previous rstore points). Then run your AV to scan for the Trojan again, and let your AV remove it.