Resizing photos when posting on the web: is there a way?

Hi,
I wonder if anyone can help me, please. I'd like to post photos on a website, but many folks there are on dial up and have requested that I compress the photos. I'm assuming this means making them smaller? LOL! I don't know!

Most of mine are stored both on my harddrive in My Documents ( I read Palmbob's low virtual memory thread with great interest as it applies to me too) and the same photos are on Photobucket at ~640x 480pixels ( I think.) This makes many of them an average of about 200,000 bytes in size.

I know how to resize with the irfanview program, but I do not want to have to resize and resave all those photos on my already very crowded harddrive. Nor do I want to permanently resize them on Photobucket because my vision is bad and want to see my photos without a magnifying glass!

The method used on the website in question is something like this:
A little icon is clicked to insert an image into a post.
A box pops up asking for your photo URL.
Insert the photobucket URL and submit.
In the post, the forumla shows up as [img] photo's URL [/img and ends with another ]

Is there a means to insert a size into that formula, as there is when using the *img src*... "tag" formula?

I hope you can follow me, and thank you for any help.
Pooch