I just recently did this myself by following roughly these steps:
1. Download the ISO.
I started with the 64 bit version and tried to install it. The 64 bit version is installed on an ISO image that isn't directly compatible with Bootcamp though, which caused me some problems (Basically a dialog when booting the DVD which asked me about the CD-ROM type or something along those lines). There are apparently ways to make the 64 bit version work by reimaging the ISO into a compatible version. I simply couldn't be bothered to solve this, and simply downloaded the 32 bit version instead.
In your case, I believe you have the 32 bit version since you mention the 2.4GB file. I think the 64 bit version was slightly over 3GB.
2. Burn the ISO
Right-click (or cmd-click) on the iso file, and open with "Disk Utility". In the app that appears, select the ISO image on the left side and click the "Burn" button on the toolbar at the top. Insert a blank DVD, and start the burning process. (I personally skipped the verification since I was anxious to get it working).
3. Repartition your drive
Make sure you have current backups of your data, as this can potentially crash your drive (Not likely, but better safe than sorry).
Open the Bootcamp Assistant (Found in Applications->Utilities). Move the slider to create a partition for your Windows install. There are some limits built-in. I created a 75GB partition which is enough for my purposes. It takes a few minutes to resize the partition.
4. Start the install
Click the button in the Bootcamp Assistant that starts the installation process. Make sure you have the install DVD in the drive when you reboot.
5. Installing
You should end up with the standard Windows 7 installation window here. At the point where you select what partition to install on, you'll see one marked with "BOOTCAMP". This is the new partition you created in step 3.
Now, Windows 7 will refuse to install on this partition by default, so you'll need to format it (There's a button or keyboard shortcut that allows you to do this). Picking the wrong thing to format here might mess up your OS X installation.
That's pretty much it. The installation process is very straightforward after this. Most things work just fine straight up. I've not managed to get Bluetooth to work, and I updated the graphics drivers to the latest ones from AMD/ATI.
Finally, you might want to make sure you have a USB keyboard at hand. My bluetooth keyboard (Logitech diNovo Edge) isn't recognised at boot-time, so there's no way for me to switch back to OS X without a USB keyboard connected. To save you some trouble looking it up, you switch between the different systems by holding down the Alt button at boot. This gives you a menu where you can choose to boot into OS X or Windows.
