Get DashLaunch 2.21 from Xbins and install it.....After installing it, all games will work without any problem, and you'll never get another prompt to install a mandatory software update.
No need to get worried on small things like these.....Just be cool
And by the way, there is no difference between a Jtagged console software wise w.r.t different motherboards. Therefore, even if you have a Jasper 512MB or 256MB or 16MB or a Xenon, it won't effect the software that runs on the console. All that you need to be careful about is the Dashboard version.