you could record a photoshop action, which is then repeatable and you can employ for batch mode (although i believe irfanview should do this as well, if i'm not wrong)
however you may wanna give both methods a try and see which yields better image quality to filesize ratio for you. (especially if image quality is paramount, if not i really think irfanview might be much less complicated)
here's the step-by-step for photoshop:
open an image.
click New Action in the Action Panel Window
click Image -> Image Size
set the width to 300 pixels (or whatever your required settings were)
use the option Bicubic Sharper (Best for Reduction)
Finally, Save for Web and Devices, to a folder you've premade before, say C:\resizedPhotos, do not rename the file, and find a level of JPG quality you require.
File, Close the image.
after that you can stop recording the Action.
now, to apply it to the rest of your images,
(i forgot the easier method of batching from just the menu somewhere but what i do is this
drag the entire bunch of images into photoshop.
then with the Action you just created selected, click Play. and it will automatically repeat the action for each image, so you just gotta jab the play button repeatedly until all the images are done.
