An excellant book to introduce you to n-tier architecture/programming is 
Rockford Lhotka's Visual Basic 6 Business Objects (you can find it on this 
site). I found that programming for n-tier applications takes an entirely 
new "mind set". Initially I found it difficult to comprehend and more than 
once I was tempted to return to my old ways of programming. I'm glad I 
persisted though as this is truely the way to go.

Good luck,
lance