I know the problem - I wrote a script which correctly installs all the required VB DLLs - but that's about 1.2 MB.
Instead, I redistribute the Microsoft VBRUN60.EXE - only 1.0 MB.
I have VB-Run 6.0 SP 5 (most sites have older versions) on my website http://www.tibed.net/files/vbrun60.exe
If you extract it to a temporary folder, run it with the /Q quiet switch, all will be well.
WARNING: install them as the last thing! This file will ask the user if he wants to restart the computer if it updated system files - and the rest of your installer won't get executed (that gave me a headache - only found out after 4 months).