Hello,
We have our network attacked with trojan, and we can detect it with kapersky, but Avast! not yet.
How can we submit virus sample so we can immediatelly get update from Avast! because we using Avast in most of our PCs.
Welcome to the forums, wahyu. 
At the bottom of the avast! web page at this link …
http://www.avast.com/eng/technical_support.html
… is the following paragraph.
If you have any suspicious files that are not detected by the latest version of our antivirus programs, you can send them to virus@avast.com. The ideal way to send such files is to compress them as a ZIP with the password 'virus' (so that the attachment is not deleted by some other antivirus software on the way).
I hope this helps you.