join-performance problem

Hi,

I have problem using joins: there are indexes which could be used, but
sequential-scan takes place;
see:

>explain SELECT b.Kdnr, date_part('year', b.Datum), d.Name, e.Name, a.Menge
,
> a.Rabproz, a.Netto - (a.netto * a.rabproz / 100),
> a.Netto * b.kurs - ((a.netto * b.kurs) * a.rabproz / 100), 'RG'
>FROM Faktzeilen a, Fakt b, Artikel c, Kollektion d, ArGruppen e
>where a.Fanr = b.nr
> and c.nr = a.Arnr
> and c.Kollektion = d.Nr
> and (c.Gruppe = e.nr or c.gruppe = 0)
> and b.kdnr = 49736;

>NOTICE: QUERY PLAN:996" 9L, 376C written
>
>Nested Loop (cost=17.08..265.50 rows=30 width=152)
> -> Nested Loop (cost=17.08..90.50 rows=5 width=115)
> -> Nested Loop (cost=17.08..66.32 rows=5 width=78)
> -> Hash Join (cost=17.08..42.14 rows=5 width=51)
> -> Seq Scan on faktzeilen a (cost=0.00..20.00
rows=1000 width=35)
> -> Hash (cost=17.07..17.07 rows=5 width=16)
> -> Index Scan using fakt_tbkundentbfakt_key on
fakt b (cost=0.00..17.07 rows=5 width=16)
> -> Index Scan using artikel_pkey on artikel c
(cost=0.00..4.82 rows=1 width=27)
> -> Index Scan using kollektion_pkey on kollektion d
(cost=0.00..4.82 rows=1 width=37)
> -> Seq Scan on argruppen e (cost=0.00..20.00 rows=1000 width=37)
>
>EXPLAIN

my problem is the sequential scan for tabel faktzeilen (which has 250000
rows);
the following indexes exist:

primary index: fanr, znr
index2: fanr
index3: fanr, arnr, arname, pknr

can one tell me why index2 is not used for the join?

Thanks in advance

Wolfgang