performance issue with distance function

I am trying to execute the following command:

SELECT R.*, distance(L1.lat, L1.lon, L2.lat, L2.lon) AS Distance
FROM Restaurants R, Locations L1, Locations L2, FoodTypeRestaurantIDX FTR
WHERE R.Zipcode=L1.Zipcode AND L2.Zipcode = '93705' AND R.Delivery=true AND
R.RestaurantID=FTR.RestaurantID AND FTR.FoodTypeID=1 AND distance(L1.lat,
L1.lon, L2.lat, L2.lon) <= 60
LIMIT 100 OFFSET 0

I would rather execute this command: (but i get the error "Attribute
'distance' not found")

SELECT R.*, distance(L1.lat, L1.lon, L2.lat, L2.lon) AS Distance
FROM Restaurants R, Locations L1, Locations L2, FoodTypeRestaurantIDX FTR
WHERE R.Zipcode=L1.Zipcode AND L2.Zipcode = '93705' AND R.Delivery=true AND
R.RestaurantID=FTR.RestaurantID AND FTR.FoodTypeID=1 AND distance <= 60
LIMIT 100 OFFSET 0

Having that second distance function in the "WHERE" section of my sql
statement is costing me at least 10-20 seconds of execution time. I am
looking for a solution that will speed this up. Does anyone have any advice.
Thanks in advance.

Ryan

PS. Here are the respective execution plans:

Merge Join (cost=0.00..3463985.82 rows=4342404 width=202)
-> Nested Loop (cost=0.00..3461172.63 rows=14735 width=166)
-> Nested Loop (cost=0.00..127378.88 rows=147350 width=162)
-> Index Scan using restaurantszipcodeidx on restaurants r
(cost=0.00..62.50 rows=500 width=138)
-> Index Scan using locationszipcodeidx on locations l2
(cost=0.00..251.69 rows=295 width=24)
-> Seq Scan on foodtyperestaurantidx ftr (cost=0.00..22.50 rows=10
width=4)
-> Index Scan using locationszipcodeidx on locations l1
(cost=0.00..2260.63 rows=29470 width=36)

Hash Join (cost=74.08..804150.11 rows=1447468 width=266)
-> Nested Loop (cost=0.00..326410.91 rows=2894936 width=120)
-> Index Scan using locationszipcodeidx on locations l2
(cost=0.00..251.69 rows=295 width=60)
-> Seq Scan on locations l1 (cost=0.00..664.70 rows=29470
width=60)
-> Hash (cost=73.96..73.96 rows=50 width=146)
-> Merge Join (cost=67.58..73.96 rows=50 width=146)
-> Sort (cost=22.67..22.67 rows=10 width=8)
-> Seq Scan on foodtyperestaurantidx ftr
(cost=0.00..22.50 rows=10 width=8)
-> Sort (cost=44.91..44.91 rows=500 width=138)
-> Seq Scan on restaurants r (cost=0.00..22.50
rows=500 width=138)