Yes, you could have been immediately re-infected after your reinstall.
This is gonna sound paranoid, but this is the new reality....
No Windows NT/2K/XP/2K3 machine is safe on the Internet for any length of time if it is NOT patched for the RPC/DCOM vulnerability.
No one!
So, if you did not install the patch before going back on the Internet, then you have been either re-infected, or the infection tried and failed and, in the process, managed to mangle RPC.
So, get the patch, burn it to CD, patch your system, and run one of the tools that gets rid of the virus.
This virus does not write to the boot sector or anything like that. There is only 1 file to delete, and 1 Registry entry.
hope this helps