is there any places in new vegas with lots of good guns? i found the place in the strip with the energy guns on the table but im after some full auto machine guns or something and whats the best place to find mods for the weapons?

Gun Runners just east of Freeside often has mods and then Alexandor at Trading Post 188 seems to carry around more mods then most but you need 40+ Guns skill or he won't have anything to do with you, don't know where to steal any good guns though.

Vault 34 has the best one, it has countless carbines, 10mm and 9mm (also has the all american rifle). But watch out the vault is radiated and its difficult to get into the armory because of the influx of ghouls.

If you don't mind stealing, the Boomers have a ton of explosive themed weapons and almost a dozen sets of Combat Armor.