Hey, I've been wanting to play New Vegas this week, so I started playing it again, all was working fine until I got into combat with enemies, as soon as the 'DANGER' came up I had horrible lag, I managed to kill the enemy and the lag went away immediately.

I thought nothing of it, but this now happens every time I engage in combat...

My computer can run the game on max, but to make sure, I've tried running in low but the insane lag is still on in combat, I've even searched the Internet and it seems people with better computers than mine have these problems

Any solutions?

Upgrade your hardware.

Recommended System Requirements:

* Windows XP/Vista/Win7
* Intel Core 2 Duo processor (or the equivalent AMD Phenom)
* 2 GB System RAM
* Direct X 9.0c compliant video card with 512MB RAM
(NVIDIA 8800 series, ATI 3800 series)
* 10 GBs of free hard drive space

I have...

Windows Vista
Intel Core 2 Duo @ 2.5Ghz
4GB RAM
HD Radeon 5770 Series Graphics Card

I think I can run it and this is not causing the problem, as it only happens in combat.

What framerates are you getting? Did this just start happening? Are you using any third party mods from nexus?
Does this happen when you start a new character?