Also, unless you have an antique IBM PCjr or something, the controlling factor is your connection speed, not your processing power. I downloaded the game pretty quickly - less than an hour - because I have the second-highest speed tier offered by my cable provider. If you're running DSL, your time will be significantly higher, but you're probably used to waiting anyway.
------------------------------------------- I'm old enough not to care too much about what you think of me --
But I'm young enough to remember the future, the way things ought to be... - Rush, "Cut To the Chase", Counterparts
You can speed it up by going into options and making sure "Disable On Demand Patching" isn't checked. This will mean some very long loading screens as the game downloads missing assets, and that can be bad when you're loading into group content and your group is fighting shorthanded while your game patches.
But since there's a lot of stuff like tons of random exploration maps that you're unlikely to ever see, there is the advantage that your install folder will never get as big as somebody with on demand patching off.
The servers are quite slow and under powered. Even with an awesom internet connection, it's going to take it's time. Just wait until you have to patch after installing. That will take you even longer because Cryptic and PWE are too lazy to update the installer.