|Depending on your motherboard you need to repeatedly tap one key during the start up in order to access your BIOS set up. This key can be the delete button or one of the F buttons along the top. All you need to do is set the boot order so that the DVD drive boots first, put in the install disk and allow it to boot to the installation. If there is only one drive connected, then the install is simple, but I would personally choose 'Custom' anyway and 'Format' to do a quick format before you begin the actual install.|
If you are running Windows 7 in the 32bit version, it will only formally recognize only a little over 3GB of memory (yours: "have 3.24GB of ram") but I understand that the RAM reserved for swap space and for any integrated graphics will come out of the total installed memory (4GB?) so you will not loose any more there.
If you are seeing CPU usage spike when opening a program like Firefox, that is normal. After it is fully opened and any page is loaded, that should go down. Also consider what else is running, your antivirus program is active and will also increase activity when loading a web page (even your home page) since every packet that is received needs to be scanned. And everything uses memory, the memory used you posted is not of any concern, it is not high.
Remember this, As soon as you finish loading windows you need to load windows 7 compatible drivers for your hardware (all of it) starting with the motherboard drivers, then video, optical drive, etc. for your system to operate properly and efficiently. Then you update windows, then you install your antivirus program (try Avast free). Once everything is running correctly, shut down and reconnect your other drive(s), format if needed and proceed to install your programs and move your files back (or shift your files before formatting if the files are on the added drive). I find that naming drives reduces confusion later.
You have to be a little bit crazy to keep you from going insane.