Firstly, a quick guide to your target sizes:
For simply providing an illustration in an e-mail, a file size of around 30Kb ( = 0.03Mb) to 50Kb (= 0.05Mb) is probably fine. For a better screen image, aim at around 80Kb (=0.08Mb) to 150Kb (=0.15kb). If you want the recipient to get a reasonably good quality print, at postcard size, aim for 200Kb (=0.20Mb).
Next, I note that you say that you had the photographs taken, rather than taking them yourself. That's relevant because, if you own a digital camera it almost certainly came with some software which will do exactly what you want. (Use the help file to look up 'file compression' or 'resizing').
Assuming that you've not already got any suitable software, download Irfanview. It's a free picture viewing and editing program:
http://www.irfanview.com/
Open an image in Irfanview, then go to Image > Resize/Resample. You'll see various options but, if you simply want the recipient to see a reasonable on-screen image, I suggest selecting '640 x 480' and clicking 'OK'. Then go to File > Save as. (
Don't just use 'Save'!!! it will over-write your original file!!!). Select a new file name (e.g. add an X to the end of the file nane, so that sunnyday01 becomes sunnyday01X) or alternatively a new location for your smaller file. You'll also see a slider which lets you adjust the compression level. By default, it's set to 80; you might as well leave it there unless you want very small file sizes. Then e-mail your new file.
Chris