How can I check...

...to see if the graphics for my game is set all the way up? I have no clue how to check and see what DX version its using and what the texture resolution is at and stuff like that...

To find the maximum texture size, you can either research it on the web starting here or run a small, simple experiment. Create a new model (add a primitive cube) and change the texture size to 1024x1024 and apply the texture to this cube (2-sided or MDL mapping, depending on your version). Be sure that you don't create mipmaps or it'll skew the results. If that loads just fine, increase the texture size to 2048x2048 (again, without using mipmaps) and test run again. If that still works, then try it with 4096x4096. If that still works, then the last one to try is 8192x8192 (caution - at 24-bit color, this uses 192 MB of memory). As you continue increasing the texture size, the last working one is the maximum supported texture size. That is, if it works for 2048x2048, but doesn't for 4096x4096 (getting an error saying it can't create D3D texture of width 4096 or the related), then the limit is 2048x2048.

To check the DirectX version, access the control panel for your copy of Windows and double-click "system". It's stated on there. For setting the resolution, use the display option on the control panel instead. This, however, only affects the resolution and color depth for running Windows, and not games. For setting the resolution in games, you'll need to use either video_switch, video_set (be cautious about this one), or setting a default by adding this to the start of your script:

var video_mode = 8; // 1024x768 resolution

For running at the really high resolutions, like above 1280x1024, you'll need a big monitor. Smaller monitors don't support very high resolutions. Here's a rough idea on what each monitor size supports:

13-inch - 1024x768
15-inch - 1152x864
17-inch - 1280x1024
19-inch - 1600x1200
21-inch - 1920x1440*
22-inch - 2048x1536*

* From what I've seen, only CRT monitors support these. The highest I've seen for LCD's is 1920x1200, but that's widescreen format. For nonwidescreen, it's 1600x1200.

I'm completely unfamiliar with widescreen resolutions - I never use them. Thus, I don't know what the widescreen equivelents are.

How do you change the texture resolution?

Just load an image file with that resolution. Take out MSPaint, set the image size to 1024x1024, bucket fill it with one color and save it. Then import this image into MED, delete any created mipmaps, and save the model. If this works, use the next larger image size, 2048x2048 and repeat. Note that they are always a power of 2. Textures should always be a power of 2 for the width and height (but it doesn't have to be a square).