Well, I'm gonna try to supply a basic tutorial for people with default programs.
I'm going to use windows purely, I don't know much about default apple graphics programs aside from the fact my sister seems to think the only default graphic program on it sucks.
Now, I use Vista, so some options might be slightly different for xp users but I'm going to assume their in the same general area. I'm also not a paint expert, so if someone else knows the program better by all means.
1. To take a screenshot in game just hit the Prt Scrn(Print screen) buttom. It will be to the right of the F12 key.
2. Windows comes with Paint. Paint can be found under all programs -> accessories -> Paint(a cup with a paintbrush in it). If you're using xp, then it might be program files. It will have program in the name however.
3. Paint is open. Now we need to open one of the screenshots. To find the screenshots, navigate to Documents -> Guild Wars -> Screens. That's where mine is anyway, if you can't find it simply do a search for Guild Wars and a Screens folder should appear momentarily. That will tell you where to find it.
4. Pick the screen shot you want to use. It will be fairly large. We don't want it to be that large, so we need to cut out the portion we want. On the right there is a toolbar with various pictures of different tools. It would probably be good to play around with these to see what they do and experiment a little with what Paint is capable of. I personally don't know, I use photoshop, so don't ask me. In the top right hand corner of this tool bar is a rectangular shape box. Pretty much a selection. When you make your selection, hit ctrl+c.
5. Make a new file by going to File -> New
6. Hit Ctrl+V to past the picture you just cut out. It still might be fairly large. So, we'll need to shrink it. You can do this by clicking on one of the eight tiny blue boxes around it's edge that appear when we click it. I suggest using the one in the bottom right hand corner. That will allow you to shrink both height and width at the same time. Shrink it to what you think looks about right. It will probably be pretty small by comparison. This is fine.
7. Now we have a big area of white by our picture. We want to make the white disappear. To do this we need to change the canvas to the correct size for what we're doing. So go to image -> Attributes. This will give you a box. This box will have two values for height and width in it. Now, close that window. It will be easier just to click the white area and shrink it to fit over your image. It works the same way as the image, just click in the white area and more tiny blue boxes should appear around the edge of the white area. You can use attributes to check the size. The general size of avatars most places is 130 x 130. This site has limits of 150 pixels wide and the height cannot exceed 200 pixels.
8. Now, with a little playing we should have a rather basic avatar or signature. You can use other tools, such as the text tool to add text to it or do other more elaborate things.
9. Finally, we want to save it. You can save it as a JPEG or PNG. I'm more fond of png myself.
10. On this forum uploading options for the avatar can be found under profile -> right below the navigation bar will be a list of links to various places, avatar and signature can be found here. For your avatar simply browse and find the image you'd like. If it rejects your image it might be too big data wise and in such a case you can save it as a different file format or shrink it some more.
11. For a signature, you will need a hosting website like photobucket or imageshack.us. Beyond that I don't appear to be familar with this board's way of doing things.
A note, when downsizing an image it's best to try and keep it's original dimensions more or less in tact. Squishing or stretching your image generally has a poor look to it.
With that, I'm also a photoshop user and probably won't mind making avatars/signatures. Just supply the picture and tell me what you'd like and we'll work together.
Fairly old stuff:
http://img27.imageshack.us/my.php?image=topaz2copyck0.pnghttp://img238.imageshack.us/my.php?image=exportwizard3xd7.png