So this is the program you used?
http://www.program4pc.com/image_editor.html
I checked it out and, yeah, it seems that for the sake of simplicity they didn't include any options when you save images. Which is kind of atypical from the norm. Nice little program, but not very good for serious image editing.
And while Photoshop is great and all, not all of us can afford it or *ahem* *cough* easily obtain it by other means.
Seriously, check out the Paint .NET program I mentioned earlier. Or grab GIMP. Either one is really good for a free paint program. Though if you got that Corel program working, their stuff is pretty good too.
Now with that all said, if you can't get .TGA importing to work then save your pictures as .PCX files instead. DEdit can also import .PCX images. I even tried importing a .PCX saved from PC Image Editor, and it worked. No need to worry about a compression setting or anything like that.
So then, you ask, "why didn't you tell me that in the first place?!" Because it's better to work with .TGA files if you can. They support alpha masks, while .PCX files don't. Later on as you get more ambitious you might start wanting to make your textures transparent, and that's where alpha masks and .TGA files come in. It's best to start working with them now, already. Otherwise you're just going to hit this same road block later on, anyway.
You
can load two separate .PCX images (one the main image, the other the alpha mask), but like xistence said it's more hassle.