I've just done a bit of Googling to try to find out what you can do about 'open with' not appearing when you right-click. Unfortunately, while it seems to be a well-known problem, all of the solutions I've found involve editing the registry, which can be extremely risky if you don't know exactly what you're doing.
It definitely is a registry error though so, if your laptop came with a 'recovery' disk, it might be worth running it to try to fix the registry. (Otherwise it might be worth contacting the firm who supplied you with the laptop. The chances are that this fault has been there ever since Windows was installed).
Alternatively, if you want to have another try via the Control Panel route, here's how to do it. (These instructions are based upon Windows Milliennium but I think XP should be similar):
In 'Folder options', click the 'File types' tab
If PPS appears in the list, click on it to highlight it. (If PPS is not listed, click 'New', type 'PPS' in the box and click OK).
Click 'Change'. You should now see the 'Open with' panel. If PowerPoint Viewer is listed, click on it. (If it's not listed, choose 'Other', navigate to the location of the program file and double-click on it).
Click 'Apply'
And if that still doesn't work, try re-installing PowerPoint Viewer. It should automatically associate itself with PPS files. You can download the installation program here:
http://www.microsoft.com/downloads/details.asp x?********=048dc840-14e1-467d-8dca-19d2a8fd748 5&DisplayLang=en
Chris