Cable giant Comcast said Monday that it is in talks to buy the 40-percent stake in the cable network E! Entertainment Television that it does not already own from the Walt Disney Co. It did to disclose its offer, but analysts estimate that the cable network is worth between $2.5 billion and $3 billion. Comcast took over control of E! in 1997 when it bought the stake owned by Time Warner and brought in Disney as a partner.