Rather than reposting everything: http://www.stealthbot.net/forum/index.php?act=ST&f=76&t=14075&st=0#entry139296

From the assembly, it looks as if SID_CHECKAD in the older product's use 0 instead of an actual product ID.  Can anyone verify this or tell me where I went wrong?

No no no, it's not 0.  When Battle.snp is called to connect to Battle.net, there's a struct passed over which contains the product id it's going to use.  It's stored in that dword you see which is set to 0.

[code]
.text:19014DC3                mov    GameTag, eax
[/code]

Set a break point on that line when you connect to Battle.net on either Starcraft or Brood War.  You will see eax contains either 'STAR' or 'SEXP'

Edit: I named 'dword_19033B90' to be GameTag.