You can't edit or delete your own replies here due to the potential for abuse, but you can always ask a moderator to delete it. Since you haven't reposted yet, though, I'd be happy to answer your question here.
Years ago Dell, HP, and others would consider it a violation of your warranty if you even opened the case, and refuse to help unless a certified repairman authorized by that manufacturer was the one who did the deed. Now, however, you are pretty much given free reign to perform your own upgrades. However, there are some basic ground rules:
1.) Your warranty will not be invalidated.
2.) You can make any upgrade you wish, except for the motherboard which would invalidate your copy of Windows.
3.) Any components you install are not covered by Dell's warranty.
4.) If any part is damaged by the upgrade process or one of the components you added Dell is not responsible and will not cover the damage.
5.) Dell will provide limited support for the installation process but that's it. If you can effectively rule out the upgrade as a cause of future problems it's best not to mention it to Dell support, as their first step would be to have you remove it.
As for the risks, the biggest is electrostatic discharge. Static buildup can damage components such as your RAM and graphics card, so if you do open the case it's best to keep off carpeting, wear clothing that doesn't produce a lot of static, avoid shuffling your feet, and ground yourself. For that purpose you can purchase a grounding strap for your wrist at under $5. They also have anti-static mats, workbenches, etc, but that's typically unnecessary. Also, use demagnetized screwdrivers and other tools whenever possible. Aside from that it's just the basics...turn off and disconnect the power first and make sure everything it seated firmly but without applying too much pressure. (You don't want to break anything.) The initial fear of damaging something can be intimidating, but it's really not that bad as long as you take your time and follow the directions.
Hope this helps,