If your 2600+ is a Barton core, then most likely yes it has its multipliers locked. If its a Tbreb core, then no it most likely you will be able to change the multiplier on it. Good Luck
You can check it will cpuid or cpu-z. The Barton core has 512kb of L2 cache, and the Tbred has 256kb of L2 cache. You can also tell by the clock speed, the Barton 2600+ is at 1916mhz (11.5x166), and the tbred 2600+ 333fsb is at 2083mhz (12.5x166).