Bad Query?? Extremely slow response

HEELLLLPPPPPPP. I have this query which ran less than 20 seconds on my
500mhz MS SQL 2000 server with 192 megs ram. When I try to run this on my
Postgres box which has dual 750mhz with 500 mg ram, it takes 3+ mins. If I
run from PgAdminII, the app freezes. If I use a WHERE clause, data comes
back extremely fast.

SELECT c.itemnumber, c.mbmcolorcode, c.mbmsizedesc, c.mbmrange, c.upc,
c.isavailable, c.totaloh, sum(c.mcoh) AS mcoh, c.backorder, c.oo, c.cost,
c.retail, c.feddept, c.description, c.mbmdiv, c.mbmdept, c.mbmclass, sum
(((c.mcoh + c.oo) - c.backorder)) AS totalavailable, c.pending_picks,
c.pending_putaways, c.transfer_suspense, c.reserved, c.oo_lt_30_days,
c.oo_30_60_days, c.oo_gt_60_days, c.last_receipt, sum((c.totaloh -
(((c.pending_picks + c.transfer_suspense) + c.reserved) + c.backorder))) AS
avail, s.pid
FROM (cheshire_data c LEFT JOIN sku_non_inh s ON (((c.upc = s.upc) AND
(c.itemnumber = s.itemnumber))))
GROUP BY c.itemnumber, c.mbmcolorcode, c.mbmsizedesc, c.mbmrange, c.upc,
c.cost, c.retail, c.feddept, c.description, c.mbmdiv, c.mbmdept,
c.mbmclass, c.totaloh, c.backorder, c.oo, c.isavailable, c.pending_picks,
c.pending_putaways, c.transfer_suspense, c.reserved, c.oo_lt_30_days,
c.oo_30_60_days, c.oo_gt_60_days, c.last_receipt, s.pid;

SCAN>>>
Aggregate (cost=117164.97..130210.52 rows=18636 width=189)
-> Group (cost=117164.97..128812.78 rows=186365 width=189)
-> Sort (cost=117164.97..117164.97 rows=186365 width=189)
-> Merge Join (cost=0.00..55710.79 rows=186365 width=189)
-> Index Scan using xie2cheshire_dataitem on
cheshire_data c (cost=0.00..8003.01 rows=186365 width=161)
-> Index Scan using xie2sku_non_inhitm on sku_non_inh
s (cost=0.00..5774.53 rows=190048 width=28)

Any suggestions would be greatly appreciated
TIA

Patrick Hatcher
Macys.Com
Legacy Integration Developer
415-932-0610 office