If you're using SQL server 2008 and later the MERGE command does that and more:
-- @member_id, @member_group_id are the ids of the record you want to match
merge blastermembers as target
using (select @member_id, @member_group_id) as source (member_id, member_group_id)
on source.member_id = target.member_id
and source.member_group_id = target.member_group_id
when matched then
update set name = @name -- etc
when not matched then
insert (member_id, name, member_group_id)
values (source.member_id, name, source.member_group_id);
Edit: @swasheck mentions problems with merge when using some indexed views in unpatched servers, or on old servers. This should not prevent you from using MERGE which is the right command to use and has the advantage of not requiring a transaction.