I managed to get client.dll to compile from SDK version 2.2 with VS6 (don't know the service pack, if any), but instead of the standard 95kb it came to 2Mb or something. More importantly, HL couldn't read it (the error message was literally "cl_dlls\client.dll cannot be read", don't you love helpful error messages!).
I've several years coding experience with C, Java, C#, PHP, etc. so I'm not a complete n00b but I'd like to get into this. I know it's not much to go on but any idea what's up with that?