I used a 70-200mm f2.8 IS L o my 400D and didn't have any problems in sinking yet more money into it when upgrading to the 70-200mm f2.8 IS L MII on the same 400D body. Glass before bodies the lens is fantastic and certainly no problem at all on a crop body*
I would strongly suggest getting a battery grip for the camera body if you don't have one already. Not only does it make portrait aspect shooting a lot easier, but it also adds a larger grip to the body for helping balance out the lens. Even if you have small hands the grips make a difference and I've never yet needed nor wanted to take my battery grip off since getting it.
An E1 wrist strap also helps.
*most of the "its no good on a crop body" arguments fall into one of two categories:
1) The person saying this is used to 35mm/fullframe angles of view and thus any lens on a crop body looks wrong to them for the stated focal lengths. To people aware of this and also with no experience of 35mm/fullframe its an invalid argument.
2) The wide end isn't wide enough on crop for a walkaround. This is typically reserved for the 24-105/70mm lenses are is a personal preference on how wide people want to go at the long end.