ok, i'll keep it short:

1. adjust 1 picture for the web

-open picture in ps
-menu file -> save for web
-in the right button, choose the 'size' tab and resize it so it will fit on a screen. if width and height are both lower than 400, leave it. if i won't fit on a screen, change it so it will.
keep in mind that a lot of people still hava 800*600 resolution. don't save the image at a 1000*300 resolution and then embed it in your website with atributes width="200" or something like that. sure, the size will be right, but it'll load a lot slower than it has to
-in the right top somewhere, click the arrow and choose the 'file size' option. pick a file size (i'd advise something in the region of 60kb and lower for regular pictures) and choose for the auto select jpg/gif option. click ok and save the picture!


2. adjusting a lot of pictures.
somewhere in the 'file' menu, you'll find an option to create a picturebook. (in the export submenu i think if i remember well, haven't got ps right now)
choose that option and in the drop down menu, choose 'large images'
now you can adjust the size. i'd advise you to make the length & hight both smaller than 600.
set the quality to 85 or something like that
click ok.
now you have an image album. but you can just throw away the html file and the little gifs for the arrows if you don't need them and want to create your own webalbum, the pictures are in a subfolder. just copy them where you want them

hope that helps some people out. slow loading images are a bitch. a lot of users will just leave your site if it goes too slow.

i've heard a lot about that, but i've never gotten around to actually doing it, but then again all my grahpics are made to be large, such as desktops and banners, but is it able to keep the same res. of say a 1600x1200 document? but compress it optimaly?

If you use your for printing, jpg is no good, well you are doing 1600x1200 images is pretty big for banner images, if you still save in jpg format you must adjust slider of compression until you find the best relation between quality and size, if you use photoshop, it shows the image in real time the degradation as you move the quality slider.

If you want for high quality images I recommend PSD (Photoshop Format) or TIF (Tagged Image Format) format, both support layers and they have lossless compression it mean they compress the image without quality loss.

you could use the 'save for web' option to compress your desktops, but then i advise you pick a file size of about 200kb or something like that. it's still a fast download and you'll have better quality.
what i use it for is pictures that are immediatly displayed, embedded in the site. in that case it's more important that they load lightning fast...