Subtitles to appear in letterbox?

[chimaera15]

I'm converting a divx to svcd with subtitles, but the end result shows the subtitles on the image instead of the letterbox...I understand that the letterbox is not part of the image and that the subtitles can only be applied to the image, and from what I understand I would have to encode letterbox as part of the image, but how can this be done? I don't mind sacrifying file size by encoding them..I am using ffdshow to display the subs

Thanks.

[toysoldier]

I use avisynth2.5 script,
my original divx is 500X280
i write a script like this:
-------------------------------------------
avisource("d:\??????.avi")
addBorders(0,100,0,100) # change original avi to 500X480
-------------------------------------------

then edit subtitle and change its name same with avi,
use MPC open avi, subtitle will auto display in pic's bottom.