SpiralRunner, take a look at the archetypes that UmaroVI created for 4th Edition:
http://forums.shadowruntabletop.com/index.php?topic=4495.0The closest to what your describing in probably Ronin. Your end result isn't going to look the same because Umaro was using Build Points instead of karma, but the stats and the gear will at least give you an idea of what a decent street samurai will look like.
The next step is to download the excellent Chummer 4, which will help with the math and playing around with the various options. You can do so here:
http://www.chummergen.com/dev/chummer/Chummer.zipOnce you have that, all of Umaro's archetypes are available for download here:
http://forums.shadowruntabletop.com/index.php?topic=4495.msg238328#msg238328Again, they won't be exactly what you want since they've been optimized for Build Points, but they'll give you ideas and direction.
From there you can start playing around in Chummer and seeing what your options are. It should be a lot of fun.
You'll probably want to spend 100 karma on nuyen (¥250,000) so that you invest a lot in cyberware, bioware, and gear, which help distinguish a street samurai from a gutterpunk.
Speed kills, so you'll want to invest in cyber/bioware that makes you faster. Look into wired reflexes and reaction enhancers. After that, you'll want things that make you better at the classic shooty-stabby combo for which samurai are renowned. Umaro's Ronin uses a customized cyberarm, which is effective, but muscle replacement (cyberware) or muscle toner/augmentation (bioware) are also valid approaches depending on the flavor you want.
Don't worry too much about picking the wrong weapon. I might suggest going with a submachine gun (the Ingram Smartgun is a good one) over a machine pistol, but that's ultimately up to you. If you're using the core rulebook and the the GM is new then don't worry too much about optimization. You should do well with whatever you select.
That should get you off the ground. Hope that helps.