Thanks for the replies.
@Juraj
Trying to do what I wrote in my last post resulted in a compile time error. Then I tried:
InfoDataSet<ForumGroupInfo> forumGroups = ForumGroupInfoProvider.GetGroups(forumGroupWhere, "");
var forumGroupIds = (from fgId in forumGroups.Items.Cast<ForumGroupInfo>()
select fgId.GroupID);
...which always resulted in an empty list. I was just wondering if there was a better way than what I've posted below.
@Swainy - I did have that initially (it does work), but I didn't like losing the property information for what I was doing.
I ended up doing:
InfoDataSet<ForumGroupInfo> forumGroups = ForumGroupInfoProvider.GetGroups(forumGroupWhere, "");
var forumGroupIds = (from fgId in forumGroups.Items.ToList<ForumGroupInfo>()
select fgId.GroupID);