Ok from what I have been able to research, your keyboard does not have a traditional Numpad setup, which is why you are not able to type the special characters by pressing down Alt then one of the number keys.
The number keys on your keyboard just relay to the same number keys at the top of the keyboard, which are not able to type the special characters. This is simply just a limitation in the keyboard that Logitech has made.
You will only be able to type the special characters by using a keyboard that has a Numlock key available on the Numpad.
However not all hope is lost. If you click on Start, then All Programs, then Accessories, then System Tools, then Character Map, you can use the character map to look up special character keys, click on them then press the select button then copy to copy the characters and you can paste them into where ever you want.
You can use the Advanced View option to search for certain special characters by name. In specfic the special characters you seem to be looking for are just a little ways up from the bottom of the Character Map window if you scroll to the bottom first.
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