Hi aka
You can use the Versions web service to get which versions exist for a File
The GetVersions method will give you an xml like this:
<results xmlns="http://schemas.microsoft.com/sharepoint/soap/">
<list id="{26E516B0-8241-4B97-984D-000000000000}" />
<versioning enabled="1" />
<settings url="http://Server_Name/Site_Name/_layouts/
1033/LstSetng.aspx?
List={26E516B0-8241-4B97-984D-000000000000}" />
<result version="@4" url="http://Server_Name/Site_Name/
Shared Documents/File_Name.doc"
created="6/7/2003 5:55 PM" createdBy="DOMAIN\User" size="19968"
comments="" />
<result version="1" url="http://Server_Name/Site_Name/
_vti_history/1/Shared Documents/File_Name.doc"
created="6/7/2003 5:49 PM" createdBy="DOMAIN\User" size="19968"
comments="" />
.
.
.
</results>
You can then just use a HTTP GET request for the content of the "url" attribute of the "result" node for the right version