Personally I wouldn't buy a HTIB, but I'm not saying they don't have their purpose. Let me also say that I just paid for my first real HT (haven't received it yet) and have been using a HTIB for the last 5 years. I can tell you now that the only reason it has lasted me that long is because it has a real receiver.
Here's why I wouldn't buy a HTIB: most are not good at all. It's as simple as that. They generally have cheap components and cheap speakers. Typically there will be a single box that does everything from play CDs and DVDs to process the sound to drive the speakers. It might be convenient to have everything all in one box with a single power plug, but you don't get the quality you do from even moderately priced separates. Plus, if something goes wrong, say the DVD player stops working what then?
If you want to look for a box setup because you feel intimidated by piecing together your own setup, or want the assurance that everything will work well together that is fully understandable. If you feel you must let me give you a few pointers.
1. don't go for the smallest or sleekest looking speakers. Try to find something where the speakers are 2-way designs so they have a woofer and a tweeter.
2. don't buy one of the all-in-one boxes. Get a unit that has a real receiver. Sometimes they'll come with a DVD player, sometimes not. Regardless if you get a real receiver you can hook any DVD player up to it, and just about any other component you want be that a VCR, cable box, or video games.
3. just because a company makes good electronics does not mean they make good speakers.
4. 3.1 or 2.1 setups that simulate 5.1/surround sound are not as good as the real thing. Plus, if you can hook up 2 or 3 speakers you can hook up 5. (the 5 in 5.1 means there are 5 speakers. 2 front mains, a center and two rear speakers. The .1 is the subwoofer)
5. If you buy something now get something with HDMI switching so you'll be ready for hi-def switching even if you don't have a HDTV now.
Now that I've gotten that out of the way let me try to talk you out of buying a HTIB, or at least buying a good one. Even if you don't want to pick out components yourself if you go to a stereo/home theater store (not a chain store like BB or CC) but a real stereo shop that sells mid-fi and hi-fi gear they will be able to help you piece together a nice setup. Then they'll be able to sell you any and all cables you'll need to hook it up and tell or show you how to hook it up when you get home. Many will even come to your house and set it up for you for a fee.
Another reason to go to a store like this is to be able to buy a 2.1 setup now and then add a center and rear surrounds later when the budget allows. This will let you get a much better system for your money.
Without knowing where you live or what shops are around let me suggest a very nice setup from av123. If you go to their forums they are currently running a very nice deal on a complete HT package. Their X series speakers have gotten a lot of praise and are some of the very best budget minded speakers available. They are currently offering a deal where you get 4 x-ls bookshelf speakers, a matching center channel, one of their x-subs, a Denon receiver and a Denon DVD player all for $999. At that price it's literally a steal. You can upgrade one of the sets of x-ls speakers to a tower if you want a more full sound. Their sales reps are very helpful if you call or email them.