Tunning T-SQL ??????

Hi
I m going through tunning part and fired query on table Code having 12500 rows

SET STATISTICS IO ON
GO
SELECT COUNT(*) FROM Code
GO
SET STATISTICS IO OFF
GO

sp_spaceused Code

got results as

Table 'Code'. Scan count 1, logical reads 60, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

Name: Code
rows : 12500
reserved: 7424 KB
data : 6272 KB
index_size: 1008 KB
unused : 144 KB

If we creat table from select * into table syntax and then create PK on the table then why there is difference in results of index_size?

got results as

Table 'TestCode'. Scan count 1, logical reads 394, physical reads 0, read-ahead reads 0, lob logical reads 0, lob physical reads 0, lob read-ahead reads 0.

Name: TestCode
rows : 12500
reserved: 3208 KB
data : 3136 KB
index_size: 16 KB
unused : 56 KB

here really index not playing part???

help me out

T.i.A