75 Million Row Update???

Hi all,
I have a table with approx 75 million rows of names and addrersses in it that I am trtying to update...so far the update is running 5 hours and with no end in sight...a liitle background is that this is running on a quad zion 500 with 3 gb ram ands one 145 gb drive (boooo) without improving the hardware needs can i improve the performance...I have indexed all the where fields that i read on and only update the table but once or twice a month, but I do daily selects by zip or county (all indexed) i even have a composite key on phone and zip...

i have heard of horizontal partioning but i always thought that was reserved for archiving old transactional data that rarely gets read on....

when i performed a trace there are plenty of reads but no writes...is this normal during an update like this...

i have been running this proc for the past 7 HOURS!!!....any help is appreciated, since all i have is time at this point....

THANKS!!!!

--Set rowcount to 100000 to limit number of updates
--performed in each batch to 100K rows.
Set rowcount 100000

--Declare variable for row count
Declare @rc int
Set @rc=100000

While @rc=100000
Begin

Begin Transaction

--Use tablockx and holdlock to obtain and hold
--an immediate exclusive table lock. This unusually
--speeds the update because only one lock is needed.
Update [2000] With (tablockx, holdlock)
set [source] = '2000'

--Get number of rows updated
--Process will continue until less than 10000
Select @rc=@@rowcount

--Commit the transaction
Commit
End