Sound Card and Graphics card advice

[Marcade]

So my computer specs are as follows following a very generous donation from a friend who thought the arcade build idea was mental but awesome 
 
 > Mainboard : FUJITSU SIEMENS D1740
  > Chipset : Intel i845G
  > Processor : Intel Pentium 4 @ 2800MHz
  > Physical Memory : 1280MBDDR-SDRAM
  > Video Card : Intel(R) 82845G/GL/GE/PE/GV Graphics Controller

I'm keeping the budget as tight as possible on this build and so cant throw money at it, but I need a sound card (onboard not working) and can't work out if I need a graphics card.
The onboard GPU is poor to say the least, but runs everything that I want to run fine, except vector games that lag badly and space invaders, as vectors are drawn differently I assume this is a GPU issue, annoyingly this motherboard only has PCI slots, not AGP OR PCI-E so I'm limited for cards too.
I'm also stuck with having to use an LCD monitor, not ideal but it looks great with scanlines added, but of course this slows it down to unplayable,  would a new card alter this or does MAME basically solely rely on the CPU Clock.

With regards to cards is there anything in particular that I should be looking around for?