if you have photoshop, follow these steps...
- open the image
- click the 'image' tab at the top
- select 'image size' from the image menu - a new window now opens
- set the resolution of the image to 72 pixels/inch
- change the pixel width of the image to 640 pixels
- click okay and resize the image
- it's now time to save the image, to do this, click the 'file' tab at the top
- choose 'save for web' from the file menu - a new window now opens
- in the drop down box with the file types (jpeg, gif, png, etc.) select 'jpeg'
- change the quality setting to 35 (out of 100 - 100 being the best quality and 0 being the worst)
- click the 'save' button and save away...
that's it... let us know if you need more help...