Five has bought a stake in Top Up TV, the pay-TV operator that offers extra channels to Freeview viewers.
The network hopes the deal will present opportunities to launch new free-to-air services during 2006.
Five is the only main UK broadcaster with no presence in multichannel TV. It got permission to launch a spin-off channel, Five.2, earlier this week.
Chief executive Jane Lighting said: "I am delighted that we are building on our relationship with Top Up TV."
"We believe it will be beneficial to both parties and to the Freeview platform. We will announce more details in the New Year."
Top Up TV chairman David Chance, said: "We have an excellent relationship with Five and extending it in this way is a natural next step for our continued growth."
Top Up TV launched in March 2004 and offers 11 extra channels, including UKTV Gold, Discovery Channel, Cartoon Network and British Eurosport, to Freeview viewers.