Does Apple or any computer store sell any cables that I can plug in my itouch directly into my modem to get a faster download speed?

How would that make the download speed faster?

Either your ISP speed or the flash memory on the iTouch is probably the limiting factor. It connects over WiFi, which in the most common situation gives you 54 megabit per second. The 54mbit is much faster than most household internet connections, but even if you did have internet that fast, the flash memory interface in your iTouch isn't much faster than 54mbit (if it isn't slower).