Hey Caio,
BTW, did you run a 'Disk Error' check on your main drive? Sounds like you've got some bad blocks on it that is keeping a portion of your drive unreadable. If existing space on your drive can still be salvaged, that's the first thing you should try.
Anyway, concerning USB or Firewire, here's my take on it. Personally, I despise USB (no really, how do you really fell about it?) Despite what the spec's say, it's slow as frozen molasses in the middle of a glacier on Titan! It's a totally consumer grade method of data transfer and should only be used by anyone trying to do anything serious if there is absolutely no other way to get it done.
Now USB 3.0 is slowly getting out there but I haven't heard any reviews on it yet. The spec's list it as faster than eSATA (I'll believe it when I see it) but the drawback is you'll need to yank your current mobo for a USB 3.0 capable one.
Firewire on the other hand is readily available and in my opinion a much faster and more reliable means of data transport than USB (3.0 withstanding.) At the moment you have 2 'flavors' such as Firewire 400 and 800 with hints of 1200, 1600 and possibly 3200 coming down the pike. However, the standard is 400 and most laptops that still offer firewire (except for mac's) offer baseline 400. You can if you have an open PCI slot on a Desktop put in a firewire 800 card to get the faster transfer rate available with some external drives made by Western Digital to name one of many.
My personal recommendation would be to go with eSATA. Either through a dedicated PCI-x or PCIe slot in your Desktop, you can add the much faster and far more stable data transfer rate and take advantage of really large eSATA drives in external enclosures or hot swappable 'toasters'.
Yes, if you are looking in your local 'S-mart' or the equivalent the consumer grade drives offered are USB 2.0 (yuck!) To get something that offers more or other options like firewire, eSATA or USB 3.0 you'll either have to go to a dedicated electronics store or shop online. Check online with reputable outfits like Tiger Direct, Newegg, Bestbuy and so on. Since you are outside the US, you may have to pay higher shipping costs and your country's import tariffs so weigh the cost of all that versus what you'll need to pay locally.
So now in answer to your question, if all you are doing is moving photos and graphics back and forth for storage, yeah you can use USB 2.0 without a lot of hassle. However, when you have to move really large files or edit and store video, at minimum you should use firewire 400 or better. Hope that helps.
