No matter what you're creating, you will probably find it necessary to edit images. Having a good graphics program that can do everything you need it to do for your creation is essential.
Features You Need
There are tons of programs to choose from, but what do you really need in a program to create sim textures?
Generally, you want to find a program that includes at least the following features:
- Layers: Whatever program you choose needs to have support for layers in your image, hopefully at different opacities and blend types.
- Brushes: You need to find a program that has a variety of good brushes, with adjustable opacity, size, etc.
- Selections: A variety of selection options, including "magic wand" selections, feathered edges, etc.
- Filters: Most programs have a filter or two, but having a nice set of many useful filters at your fingertips can be extremely helpful once you get into more advanced image manipulation.
Most any basic program will offer the features above. If you don't know whether a program has those features, try checking its website, forums, FAQs, or help documents for more information.
There is also some information on Wikipedia, comparing various graphics editors, that includes some of the information above: Comparison of Raster Graphics Editors. For a bit more readable list of graphics editors, including a larger list of free editors, see List of Raster Graphics Editors.
MS Paint CANNOT BE USED for editing graphics for Sims. It is not a graphics editor, but a toy. It does not contain the features above and simply will not create good graphics.
If you are unable to purchase a graphics editing program, you can get free ones online. Though generally somewhat more limited than pay programs, free programs allow anyone to create decent graphics with a little persistence.
Paint.NET - A simple free program with a basic, user-friendly interface. It doesn't have very many filters and effects, and is somewhat limited in layer settings and brushes, but it can do very basic editing. It has the ability to manage .dds DXT5 (interpolated alpha) built into it.
The GIMP - Another free program, surprisingly full-featured for its price of $0. It has a bit of a clunky interface which gives it a slightly higher learning curve for those familiar with other programs, but with a little patience, you can make GIMP do almost everything that the higher end programs will do. Requires an additional plugin to manage .dds DXT 5 (interpolated alpha).
Adobe Photoshop - The industry standard, and among the most powerful graphics editing programs you can have. Current versions are multiple hundreds of dollars. However, you can find earlier versions for cheap on eBay - Photoshop 7 goes for around $40 there, and really isn't that much different from the current expensive versions.
Corel (formerly Jasc) Paint Shop Pro - Also very common, and similar to Photoshop, for less money. Does not manage alpha images with anything approaching functionality.
Ulead PhotoImpact - Ulead PhotoImpact: Often included in software bundles with scanners, printers, and prebuilt computers. It's fairly limited in comparison to other pay programs... roughly comparable to GIMP, with less support. It's included in this list as you may already have it on your computer, and may be able to use it for some basic, simple editing.
If you would like to create graphics, we recommend you pick up a copy of Photoshop 7 or 8, used. The price is fairly inexpensive, around the cost of purchasing another expansion pack, and will allow you to follow most tutorials fairly well. Photoshop is used the most out of anything, has great support both in the Sims 2 community and outside of it, and even if you don't have the latest Photoshop, you should be able to do just about anything you need to with the older version.