I had a meeting at Kista Entré this afternoon, and did a bit of shopping in Kista Galleria afterward. After having no luck at two shops devoted to video games, I found this little gem at On Off, a big electronics chain similar to Best Buy.
It's Microsoft's Xbox 360 Wireless Gaming Receiver for Windows. It allows one to use a wireless Xbox 360 controller with a PC. I'm planning to use it with the controller Kelly gave me as a birthday gift last year. Now I just need to wait until Mac OS X drivers for the device become available.
In the U.S., the receiver can be found for as little as $16. I paid 250 SEK for mine, roughly equivalent to $36 — more than twice the price of the same thing in the U.S.
Oh well. At least I have it now.