There's a useful new article on http://support.microsoft.com explaining how to determine which version number of SSIS you are running and which release (i.e. RTM, SP1, SP2) it pertains to. I keep meaning to put a post like this together so thankfully now I don't have to.
Read it here: http://support.microsoft.com/default.aspx?scid=kb%3ben-us%3b942177&sd=rss&spid=2855
One point to make is that this doesn't explain how to determine which version of the client tools you are running, only SSIS itself. If you are maintaining discipline of your software installations then they should match up anyway.
-Jamie