trigger TOASTing quicker?

Hi all,

I'm in the planning stages of replacing a MySQL DB using ISAM tables 
with PostgreSQL 8.1.x on Suse 10.0.  I think that sentence right there 
will tell you why!

Anyway,  one of the columns in one of the tables is a big chunk of XML 
(500 to 500KB).  I'm not normally a fan of that kind of thing, much 
preferring storing such things in the file system.  But I see that 
TOASTing that column will address most of my concerns.  On to my 
questions:

TOASTing is automatic?  I don't have to code anything for it?  Plain 
vanilla SQL99 will work with it?  I have terrible memories of Oracle's 
LONG RAW columns....

Assuming the above is true, is there anyway to get a column's data to 
TOAST at a threshold smaller than the default of 2000B?  For example, I 
really would like any amount of data stored in the XML column to be 
TOASTed.  So I would like to be able to say something like 
ALTER TABLE foo ALTER COLUMN xml SET STORAGE EXTENDED;
ALTER TABLE foo ALTER COLUMN xml SET EXTENDED_THRESHOLD 500;


tia,
arturo