First of all, have you checked to make sure your DVD drive is at the top of your boot order in your system's bios (To check press the Delete key or F2 depending on your system to get into bios. The boot order will likely either be under advanced settings or boot. If your dvd drive is not at the top of the order, use the options to move it there).
If you burned the dvd from an iso or similar file type using a mastering program (nero burning rom, pinnacle instant dvd, ...) it should already be configured to be bootable. If you just copied the disk image onto a dvd, it will likely not work. In that case burn it again using one of the aformentioned programs, they all work just as well for burning the disk (If you have any problems using one of the programs, just ask, someone will likely know how to use it). If you got the DVD from some one else or from another source, it might work, but it is a little harder to tell.
Once you have a good dvd and the boot settings in the proper order, make sure any files or folders on your computer that you want to keep are saved elsewhere, you will erase them during a custom install otherwise.
When you are ready to install Windows 7, put the DVD into the drive and turn on your computer. After the computer displays the startup screen/post data, it will have a prompt like "press any key to boot from dvd" You then have about 5 seconds to hit a key to continue installing.
Windows 7 will display a loading windows animation/image and will eventually arrive at a screen where some options are listed. One of these should be custom install. Click this.
Accept any yes/no prompts and enter any personal preferences that may be requested during the setup process. When you get to a screen asking where to install windows, open advanced options, select your main HDD and click delete on any partition on on. Once the drive is empty, click create a partition and click ok (or enter a custom size if you want to have multiple partitions). Once that is done, you should see two partitions, plus one or more segments of free space. The second partition is for system files and should be left alone.
From this point on, let the installer do its thing, again adding any personal preferences it may request.
After a little while of installing (depends on your system) it will reboot. After this point, the installer will start asking for stuff like user name and network settings. Put what you wish or let it use the default for these. After this, it will likely either restart or go into the operating system. In either case you are finished installing windows 7.
After you are in the operating system, click the start icon (the little windows icon like in vista) and right click on computer, then select manage. Click on device manager in the computer management window. This will list any devices that the OS was not able to find drivers for. If you can get access to windows 7 drivers for these devices, use them. Otherwise, download and use the windows vista drivers for them, they work in most cases.
Good luck and enjoy using Windows 7!
