Help with templates

Hey all,

I thought I understood how templates work, but my GM just recently confused me, and not having ever used one... How exactly does the ECL/experience work afgter you've acquired a template?

For example, our 'base' argument was as follows:

An 11th lvl wizard picks up Lich, my understanding was that you are 11th level but now you gain xp as a 15th lvl and it takes you 15,000 to advance to 12th and noq have an ECL of 16th. And then you need 16,000 to get to 13th with an ECL of 17th, etc.

My GM contends that the you are 11th with an ECL of 15th, gain xp as a 15th, but have to buy off the next 4 levels before you advance to 12th, i.e. 11,000+12,000+13,000+14,000.

So needless to say, I'm a bit confused. Explanation (with page refs would be welcome).

Thanks.

An 11th-level wizard with 59,800xp becomes a lich. He is now a 15th level character with 55,000xp. He gains experience as a 15th level character and in order to reach 16th level (12th level wizard) he must amass a total of 120,000xp, that is, an additional 65,000xp (PHB p. 22, "Table 3-2 shows the experience point total needed to attain a given character level").

D@mn him for being right! Ah well...