postgres 8.3 beta 2 storage question

Hi,

1.How does postgres version 8.3 betat 2 handle varchar and numeric data types in terms of storage
I understand for varchar it has 1byte overhead (instead of 4) if length<128
How does it handle for numeric? The manual says
"The actual storage requirement is two bytes for each group of four decimal digits, plus five to eight bytes overhead." 
I dont understand how the overhead is measured here?...5 to 8 bytes?

2. Does postgres always inserts a complete record into a page unlike oracle whose record can span multiple pages? Does this waste space too?

Thanks
sharmila