Dilemma - ITM Millenium fork on Specialized Sirrus

8 months ago I bent the fork on my 2002 Sirrus and only now have
gotten around to replacing it , after some bad experiences (Wiggle
sending me a 1" instead of 1 1/8" Kinesis Crosslight fork when the
latter was sold out as if I wouldn't notice the difference).

Although I'm delighted with the Millenium, I'm not so delighted with
the compatibility issues or the lack of help from my LBS. I asked
them whether I needed a carbon bung(?) for it and they vacillated and
basically said 'pay us to install it'. What I really need to know is
whether I must and where I can get a bung and what I do with it!

Also, the Sirrus' 28c tyres are too wide for the Millenium! I've
measured the rim-to-rim distance and according to the chart at Sheldon
Brown.com I can use 25c. Can anyone tell me if this will suit the
Millenium?

As you can tell I'm a dumbass so help would really be appreciated