Another alternative way.
1. extract the DAT file from the VCD via ISO Buster, use option MPEG frames only option while extracting and give the file extension as "mpg" (without the qoutes).
2. Download the latest Nokia PC Suite, its much lighter then one bundled in CD. Use it to encode the extracted mpeg file to 3gp.
IMtoo as mentioned is not a free software, if you can afford, it'll do the job fine. But Nokia PC suite is free. For other formats try free software such as Virtual Dub.