Er, I think you mean convert between BCD and binary. VB6 never actually works in decimal at all. Even the Decimal Variant subtype is a binary format.

Can you show samples of the BCD you have there? Hex dump?

Usually it'll either be simple low-order digit first or the other way around, but since it arrives as bytes you need to know the nibble order, sign format, any padding, etc. as well.