Umn I am not exactly sure of what you are asking, but based on what you just wrote out, you have an older generation GPU, something like a 5 or a 6 series card from Nvidia or a 9 series card from ATI. Fortunetly this means that you should have a PCI-e x16 1.0 slot. If this is the case, you can pick up a lower end card, like a Geforce 430 or a Radeon 6450.
Now this all just a guess based on the vague information you gave us. To be more specific, we need the type of motherboard as well as CPU that you have.
ASUS P6I-1 motherboard, with intel cor 7 CPM 920 @2.67 GHZ. I have radeon hd 6450 1024mb GDDR3 graphics card, do not know if this card and computer will fulfill the flight simulator which requires C computer with 1.0 GHz Pentium 3/4 or AMD Athlon/64 compatible processor or better Microsoft Windows XP, Windows 7 or Windows 8 operating system 256MB system memory (RAM)
1.5 GB free, uncompressed hard-disk space
ATI Radeon 9800/NVidia Geforce Ti4200 with at least 128MB memory or better
Microsoft DirectX 9.0c or higher
DVD-ROM Drive for installation
1 free USB 1.1/2.0 port
100% DirectX 9 compatible sound card (optional)????
1) do I need a card at all, or do I need a more or less or equally powerful one?
2) It seems my computer is well suited for this flight simulator, but I am stumped on the memory or the card needed and what I have , and I do have a HD audio device and higgh definition audio device both listed under device manger?