Said The Fist:
Im using the newest version (7) for photoshop on os x ...
I've seen the save for web deal but havent tried it yet....Ill give it a whirl....
I am also on OS X and PS 7. Here is what I do and it works well.
Go to Image>Image Size.
Once there set the document resolution to 72 dpi and set the document size accordingly. Typically you will want to keep the longest size less that 7-8 inches so it can be viewed easily when posted. I have a screenshot attached below that shows the setting I use. This first step sets the size of your image.
Then I go to "Save for Web".
I use the 4-UP window. For photos choose jpeg, I use a quality setting of 65-70, try changing that setting and it will show file size in the window with the image you have selected, once you are under 160kb hit save and you are ready to attach the file. You should be able to get well under 160kb to save on bandwidth for those on dial up.
A photo service such as smugmug.com allows you to post your original files there and link to them via the IMG button. That keeps you from resizing, people can access a larger file if they want to and it allows you to post more than one image in a single post.
Let us know if you have any other questions.