Just noticed this thread as you mentioned one of my images (the one in the middle of Marisa), so I thought I might as well answer too...
The description of how that image was taken is already under the image so just some general pointers...
The main light was softened with a shoot-through umbrella which would be a cheap and simple addition to the flash you've got already.
While it's true that to some extent you get what you pay for (studio strobes recycle more quickly, are more quick to adjust, can put out more light [which you don't need with a digital SLR]), at the end of the day light is light and you can achieve a lot with a few strobes like the one you've got already and some simple light shaping tools.
The flash cord you mentioned is a sensible option to get your flash off your camera (you'll also likely find a light stand and umbrella adapter for your flash useful).
You can add a second, cheap strobe (doesn't have to be as fancy as the SB-600 if you're happy to learn setting your flashes up manually) for more flexibility.
When I'm not in the studio I use two old Nikon flashes (SB-24, SB-28DX) together with cheap Chinese radio triggers ($20 delivered for a set...). Works great and doesn't break the bank.
The site strobist.com is well worth checking out for lots of advice on lighting on a budget....
Haha, that's a coincedence
! I've seen all of you pictures if I'm not mistaken, very nice pictures. Thanks for the tips, those are some great tips. I have to start as soon as possible because from the day I posted this until now I got like 3 other requests, so I would have to do something about that. But I have some questions...Is there a difference between photo shooting with strobe lights with a soft box and photo shooting with 2 or 3 flashes with an umbrella for the flashes? I'm a little confused there, also where can I buy those 20$ radio triggers
Thanks in advance