I'm getting 2 KRK monitors and I know that the quality of the sound it's a lot better if you are using a audio interface, but my question is, would matter the computer that I have? I mean, would my laptop interfere with the audio interface? Does it have anything to do with my sound card or something like that? And I don't know which audio interface I should get, for my budget I would like to get the speakers first and then save some money to buy a good audio interface, what do you guys think?
The audio interface would be used instead of your sound card.
The laptop itself shouldn't play a role in the quality of the sound. (Though it can happen... see @left's comment below)
The sound quality will be affected by the signal chain. I.e., the original audio quality, the settings of the software you use to edit the audio, the interface you purchase, the cables used to transmit the audio, and the monitors.
Keep in mind, as you shop around, the sound quality is really only as good as the weakest link. Wouldn't make much sense to purchase super high-end monitors that are fed through a sub-par interface.