Post I wrote out last night:
Well, we'll do this item by item.
Gfx card:
Your selections sound fine, if your comp will support them. We need to determine that. Shut down your comp and open the case. Now, look on the back of the case for several slots that are about 1 cm wide and 4-5 cm long. On the board inside the case by those you will see several white slots. Look specifically at the top one (the one closest to the center of the case). Is it brownish, and not lined up with the white slots? If so, that's an AGP slot. You can look at
this pic for reference. The bottom three are PCI slots, the top brown one is the AGP slot we're looking for.
If you *don't* have an AGP slot, you're basically out of luck. You would have to replace your motherboard to get one, but you'd also have to get a new case because Dell boards and cases don't conform to ATX specs. Then you'd have to buy another power supply because the Dell one probably wouldn't fit in the new case... so you might as well just get a new comp.
Hard drive:
Are you planning on replacing your current drive, or adding the new one in addition to it? If you want to add it in addition, you need to be sure that you have an open bay to mount the drive in, and a free power connector to power it. You may also have to buy a new IDE cable to get a connector for it.
RAM:
2GB is unecessary for you. There only a very few games that would see any advantage from it- The main thing that would make use of 2GB would be if you did a lot of Photoshop, 3D design, etc... I rarely see more than 700MB of my 2GB in use.
Now, while you have the case open, find the RAM. How many slots do you have total, and how many are currently being used?
Now comes the downside of trying to upgrade a Dell. Dell uses specific types of chips in their memory, so you're forced to buy upgrades either from them or from one of the few companies that make compatible memory. What you buy from newegg will not work in your dell.
I recommend buying it from Crucial. Go to this website
http://www.crucial.com/store/listmfgr.asp?cat=RAM and go through selecting your computer. Under "Step 1" it should tell the maximum amount of memory that your computer supports. As long as it is 1GB or more, you're ok. Heck, just post what model Dell you have and I'll take a look at it to see what options you have.
I will warn you also, if your comp can support the AGP video card (and it should definetly have room for a sound card), you will have to go into the BIOS and disable the onboard sound and video before you can use the new cards that you bought. It's not difficult, but there is more to it than just plugging the cards in a playing.