CBS is doing a lot of in-house promotion leading up to the premiere – The Late Late Show with Craig Ferguson will have HIMYM stars as guests on the following dates:
Monday, September 8: Neil Patrick Harris
Thursday, September 18: Jason Segel
Friday, September 19: Josh Radnor
[By the way, Amazon's currently got a sale on S2 and S3 of Doogie Howser - both sets are $12.99. S4 is also on sale for $15.99, and S1 is at its normal Amazon price of $21.99.]