UPDATE - PowerShell 3.0 now includes a last switch for get-content
get-content <file> -last 5
To watch a log file ...
get-content <file> -wait
but not exactly the same functionality. So a better way is to get the command from Microsoft.
Tail is included in the 2003 Resource Kit and works well in Server 2008 environment.
Download tail here:
http://www.microsoft.com/download/en/details.aspx?id=17657