1. RAM - As scapegoat_44 said you should carefully look for RAM upgrades. Altough 800MHz DDR2 RAMs should work mostly in motherboards accepting only 667MHz modules because of compatibility settings in RAMs (SPD chips), but there are always exceptions. Before upgrade check your local retailer if it accepts returns in case of problems.
You can always find manual of your motherboards online and check for compatiblity as well as info about mobo in the manufacturer site.
2. Graphics card - Look very carefully at power requirements of the card you choose and compare it to your PSU wattage. You didn't specify your PSU (Power Supply Unit) Wattage and brand. There is a scenario that it could
fail and do a further damage to your computer if you put your new graphics card in.
Look for graphics card reviews and check what PSU reviewers recommend. For some general guidance look for ATI / NVidia PSU specifications for gfx cards as for example AMD HD 6750:
http://www.amd.com/us/products/desktop/graphics/amd-radeon-hd-6000/hd-6750/Pages/amd-radeon-hd-6750-overview.aspx#3
which states:
"■450 Watt or greater power supply with one 75W 6-pin PCI Express® power connectors recommended (600 Watt and two 6-pin connectors for AMD CrossFireX™ technology in dual mode). "
They are go with safety margin because non-branded PSU tend to have problems with having correct wattages and voltages delivery.
3. General idea - ask a computer geek friend (in reality I mean
) to help you if you didn't put up your rig by yourself and just want to upgrade. If you go by yourself I recommend to read some about upgrading. There are always some dilemmas which couldn't be solve by online help.
Hope it helps.
P.S.: Some guidance from AMD site about upgrading old graphics card:
http://support.amd.com/us/kbarticles/Pages/737-20870HowtoInstallYourATIProduct.aspx#header2