Add counter to SELECT query results

I am trying to add a counter to the Select result list. Keeping this simple, my query is this:

Select distinct '"'+cast((product_sku) as varchar(30))+'"' as product_sku,preco,'"tamanhoecor::' + Left(Main.preco,Len(Main.preco)-1) + '"' As "custom_price"
From(
Select distinct ST2.product_sku,

        (Select cordesc + ' - ' + tamanho +':' + cast(price_dif as varchar) + ';'
        From [mg_produtos_preco] ST1
        Where ST1.product_sku = ST2.product_sku 
        ORDER BY ST1.product_sku
        For XML PATH ('')) [Preco],
        product_price, cordesc,tamanho
        From [mg_produtos_preco] ST2) [Main]

Which gets me this:

product_sku     preco                                                custom_price
"340803 010"    Preto - S:0;Preto - M:0;Preto - L:0;Preto - XL:0;    "tamanhoecor::Preto - S:0;Preto - M:0;Preto - L:0;Preto - XL:0"
"340803 100"    Branco - S:0;Branco - M:0;Branco - L:0;              "tamanhoecor::Branco - S:0;Branco - M:0;Branco - L:0"

However, I need this:

product_sku     preco                                                      custom_price
"340803 010"    Preto - S:0:0;Preto - M:0:1;Preto - L:0:2;Preto - XL:0:3;  "tamanhoecor::Preto - S:0:0;Preto - M:0:1;Preto - L:0:2;Preto - XL:0:3"
"340803 100"    Branco - S:0:0;Branco - M:0:1;Branco - L:0:2;              "tamanhoecor::Branco - S:0:0;Branco - M:0:1;Branco - L:0:2"

I tried to use what I found here: http://msdn.microsoft.com/en-us/library/ms187330%28v=sql.105%29.aspx

I tried DECLARE @pos nvarchar (30) Select .... (@pos + = 1) .... from .... (SELECT @pos = 0) ....

but I get "Invalid syntax next to" DECLARE ". Waiting for" (", SELECT or WITH") plus "Invalid syntax near ="

I tried this code that worked:

GO
DECLARE @var1 nvarchar(30)
SELECT @var1 = 'Generic Name'
SELECT @var1 = (
SELECT AppUserName
FROM [AppUsers]
WHERE AppUserID = 1000)
SELECT @var1 AS 'Company Name' ;

I would be grateful for any help.

Thank.