For running VST, mainly galaxy vintage D

http://www.dell.com/us/enterprise/p/latitude-e6420/pd
(I have the core i7)

I haven't noticed any problems with it at all as is, but I was just wondering if an external soundcard would do anything at all that it isn't doing already.

If you're having trouble getting a grip on latency, a legit soundcard would help that. In fact I use a Steinberg CI1, which is especially good at getting the latency down really low without any clicks, distortion, or anything. And, yes, a soundcard's outputs often outperform those of about any computer.

So is that the case even if the external soundcard hooks up via USB?

The reason external soundcards (which are generally USB devices) often do better in terms of latency is simply because they come with better drivers than the onboard sound card. On a very fast computer this may not be an issue. I use an external card with a core 2 duo computer because I can't get the latency down otherwise. On my new i7 I haven't noticed the issue for whatever reason.

External interfaces may also have super electronic components, which doesn't affect the latency, but may affect the sound quality. Certainly the differences between headphone amps on computers and various audio interfaces seems to be significant if you have an ear for that kind of thing.

I bought an external sound card because of latency. As gv points out, new, fast computers likely won't have the latency issue. Mine is old (dual-core @1.7 GHz, 2006 vintage), so I had to get the external sound card.

As for sound quality ... I found the laptop audio quality (discounting the latency) to be acceptable. But I've not done an A/B comparison.

Conclusion: Buy an external sound card if the computer and its internal card (when assisted by ASIO) still fails to achieve low latency.

Yeah. Latency doesn't seem to be an issue. I crank ASIO4ALL all the way down to the smallest buffer (64). I was just wondering if I could get significantly better sound (not that I'm displeased at all with what I'm getting).

Also, are there better drivers than ASIO4ALL?

The ASIO driver generally come with the sound card.

For cards that have no ASIO driver, someone wrote ASIO4All as a generic driver that works with nearly all sound cards.

I don't know of any other such ASIO driver.