If you have an xvid movie and a subtitle file you can imprint the subs on the movie using Virtualdub. You will need some other software tools such as Subtitler and Vobsub. These are freely available for download. With these tools you can insert SSA, SUB or IDX subs. You can also download SRTtoSSA which will enable you to add SRT subs by converting them to SSA format.

Go to the menu Video>filters and tag the "add" button. This will display a list of pre-loaded filters and a "load" option. Hit load and go to where you have Subtitler or Vobsub stored and you will find a VDF file. Load this and then open it. Browse to your subs file and load it. Encode your movie and enjoy it with the subs.