They are pretty low end side-scrolling 2D games, so pretty much any PC from the past decade would play them all fine. Which metal slug game in particular?
Intel core first gen was what, like 2006? It's pretty low end but again you don't need much to play these.
According to steam something like this should work:
MINIMUM:
OS: Windows Vista, 7, 8
Processor: Pentium 4 2.4Ghz
Memory: 1 GB RAM
Graphics: Intel HD Graphics
DirectX: Version 9.0c
Hard Drive: 500 MB available space