5 main issues can cause poor images:
1) light. No camera or lens will help - you have to adjust to it or adjust it.
2) user error in any other way
3) incorrectly focused - could be an issue with the lens, body or the user
4) poor optics
5) body cannot handle those conditions well (high iso noise, locking focus on difficult subjects)
We don't know about 1-3 - ideally some examples would clarify the situation;
4 - you would certainly need so better glass to improve the output; 1000D is fairly capable body - but could reach its limits quickly when pushed hard (not sure that is the case here)
As you seem to be into the long lens territory, you could have a think about canon 70-200mm f/4 L USM, and / or 100-400 or 300/400mm prime + 1.4tc.