Some DVD's require that you install the player that comes on the DVD in order to play that particular DVD. I think they do this to defeat illegal copying of the DVD.
But.......... if you are deciding to upgrade, here are some things to consider
What will I use the computer for?
For most, the answer will be to surf the web, email, office applications (word processing, spreadsheets, database), music and video playback. If you fall into this catagory then starting with a base system (by today's standards) will be a good start. That is assuming the base system includes a CD/DVD R-w drive. If not then you would need to have that included. If you are going to be using the system for video gaming, audio or video recording or engineering applications such as CAD/CAMM, you will need to upgrade from the base system or perhaps start with high end systems.
How much do I have to spend?
Set your budjet and then go shopping. Pick the package that gives you the most bang for your buck. When selecting a system the thiings I would consider are; processor speed, storage capacity, random access memory (RAM), and I/O interface types. If you are not using this as a gaming system then the standard video card that comes on newer systems will suffice. I/O interface types includeRS-232, USB, Firewire, network, etc. Most new systems come with firewire but if it's an upgrade and you don't need it, then don't pay for the upgrade.
Which brand should I choose?
I would stick with a known name brand that has a good support structure and good reputation. Personally, I think that Dell is not a bad system. They are easy to work on and Dell''s support is pretty good. Compaq was bought out by HP and I have never liked the Compaq becuase of it's propriatary nature. Example: you need to upgrade RAM. You have to purchase Compaq's RAM and they charge you double or triple of third party OEM's. I have had pretty good luck in the past with Gateway as well. I was always pleased with their customer support but I haven't used them for several years now. There will always be somone out there that has had a bad experience with any vendor but that doesn't mean they are bad. My experience with Sony was bad but that doesn't mean they make a bad system and that doesn't mean you will have a bad experience with them. The thing I would do is stay away from those systems that you purchase from TV. I believe that is where you got your current system. The problem with those is support. Just my opinions and I hope this helps. Here are some links to a couple of offerings out there right now. Good luck and let me know if you have any questions.
Dell
Gateway
Sony
HP