Hello svennd and welcome to Seven Forums.
Great questions. Here's what I think I know about RAM. Free RAM
– It’s not being used for anything Available RAM
- That's all physical memory which is immediately available for use. It includes the Free RAM, but also includes the Cached RAM. Cached RAM
- In the geekiest sense, cached memory (RAM) is a special kind of memory that a computer processor (CPU) can access more quickly than it can access regular RAM. But some folks refer to cached RAM as the memory that's automatically set aside for hardware. For example, let's say you have a 1GB graphics card and 4GB of RAM. A portion of that 4GB is automatically set aside for the graphics card and other hardware on your computer. That's why on a 32-bit computer with 4GB RAM you'll see various articles stating you'll only have about 3-3.5GB available, give or take. Interesting previous Forum thread here
you might want to read. Total RAM
- As it implies, this is the ... well ... total of your RAM modules.
To get a better visual representation of how your RAM is being utilized on your machine, take a look at Resource Monitor. Resource Monitor
Depending on how you use your computer (heavy on video editing, or large multiple files like spread sheets open at the same time, etc.) 4GB is usually enough for most people. If and when you get a new machine, then consider getting the 64-bit version and more RAM. And as far as using any 3rd party tools to tweak RAM usage, I wouldn't bother. Windows 7 does a really nice job taking care of that all on its own.
Hope this helps a little.