There are many skeptics out there who feel that strength training has little place in the domain of cardiovascular-focused sports. I've never really been one to believe this, and I've found you don't have to dig too far to find articles that support the huge benefits derived from strength training.
The training year is long, and should consist of many parts. But past this fact is another key point - how those parts of the training year fit together.
A book I really enjoyed was Tudor Bompa's "Periodization Training for Sports". And YES it has a part on cross country skiing because this is one of the sports he helped revolutionize!
I've just discovered this little interview and thought I'd share it with you:
http://www.bodybuilding.com/fun/mahler18.htm
Enjoy your summer!