Array and Aggregate Functions

[Michael]

Hi all!
I'm new in PostgreSQL and I need some help.
I have a table:

MyTable
----------------------
ID | Price | Units
----------------------
1 | 1.27 | 12
2 | 1.12 | 22
3 | 1.12 | 11
4 | 1.27 | 10
5 | 0.99 | 7
----------------------

and I need to count amount:

SELECT SUM(Price*Units) as amount FROM MyTable

but I need knew what IDs were included in each calculated line.
My question: can I create an array and push IDs in it:

SELECT SUM(Price*Units) as amount, {ID} as ids FROM MyTable

Thanks in advanced.