Highest resolution with Nikon D40 6MP?

Largest image size I can print with the following:

1. RAW Compressed
2. JPEG Small, Medium and Large.

I want to print some wall posters.

8x10 is about the largest you could print a 6MP image at 300dpi, which is sort of the standard printing resolution. If you want to go larger than that, it's just up to you how much quality you want to lose.

Start with a well-exposed and sharply focused photograph in RAW format, and you can print just as big as you want. All you need is a printer capable of the size you want.

You don't need 300dpi for a wall poster, unless you intend to stand 4 inches from it with a magnifying glass. That is a huge (and incorrect) assumption made by just about everybody that posts here about how big you can print.

All you actually have to do, if you have a printer capable of doing so, is load the paper, tell the driver how big your paper is, and hit print. If you don't have your own large format printer, you send the image file to whomever makes you happy to print it for you. Again, you just tell them how big.

JPEG - Fine and Large it the highest quality JPEG the D40 produces

RAW can produce higher quality images when they are being processed in a program like Adobe Lightroom 3 and saved as TIFF (uncompressed) files