Steen,
This will work fine, as long as your Catalyst 2960 switch is not one of the 8-port compact models (which do not support the GLC-GE-100FX=). The 100Base-FX standard supports multimode fiber distances of up to 2km in full duplex mode.
The hardest part will be finding multimode fiber patch cables with the correct connector ends.
Your WS-C2950C-24 (old type) has 100Base-FX fiber ports with MT-RJ connectors.
The Catalyst 2960 switches use 100Base-FX SFPs with LC connectors.
The 1300nm wavelength is the targeted region of the optical spectrum. The optical transmitter on each port can transmit at anywhere from 1270 to 1380nm, and still work; but typically operates around 1300 to 1310nm.
The optical receiver on each port is sufficiently forgiving to allow the transmitters to vary 10's of nanometers from that ideal 1300-1310nm range, and still function reliably.
Cisco 100BASE-FX Small Form-Factor Pluggable Modules Installation Notes
http://www.cisco.com/en/US/products/hw/modules/ps5455/prod_installation_guide09186a008032afe7.html
Hope this helps.