Typically, I guess most people are using
Photoshop (you can download a 30 day trial from
adobe.com BTW). The easiest way to do it in PS is from the
Image menu, select
Mode and choose
Grayscale. BUT, a more controllable method is to go to the
Image menu, select
Adjustments, choose
Channel Mixer, tick the
Monochrome box, and then adjust with the sliders, that way you can get the levels of contrast and tone you want, but bear in mind that doing it this way will not change the mode, it will merely drop all the colour data out of it (so it will still be an RGB image), so you might then want to manually change it to a grayscale with the first method suggested. Unless you want to try this....
The easiest way to get a 'sepia tone' image is to create a grayscale image in one of the above ways, but keep the image in
RGB mode and then add a
new layer from the
layers palette (on the right). When you've done that, select a beige colour from either the
swatches palette or by double clicking on the
foreground colour at the bottom of the
left hand toolbox and picking a suitable colour. When you've got a good sepia colour, choose the
paintbucket tool (it may be behind the gradient tool on the toolbox, click and hold to switch tools) from the
toolbox and
click in the image area, it will initially flood the image with a solid colour, but go to the
layers palette on the right and change where it says
Normal, to something like
Overlay or
Multiply and play with the
opacity slider just to the right, until you have what you want. Then try
flattening the image from the
Layer menu and going to the
filters menu and selecting
Noise,
Add Noise, or maybe
Despeckle.
Note that you have to flatten an image to be able to save it in several of the modes, otherwise you'll be limited to saving a layered file in either PSD or TIFF format (and one or two other wierd ones). For more info, do a search on google or yahoo for 'Graphic Formats Wiki', this will take you to a wikipedia page which explains most picture file formats and what they support.
Have fun.

Chock