changing null-values' sort order

hi list

coming from the MS-SQL Server world, we're migrating our applications slowly to pgsql 8.1. now we thumbled on a problem with different sort-order behaviours:

we got a table with dated records:
table: votes (v_userid, v_date)

the v_date field can either be null or a date in the past. in mssql, sorting the table to list records in descending date-order

select v_date, v_userid from votes order by v_date desc

produces a list where first the records with dates are listed, and then the ones with nulls. in pgsql, the null-records are listed first before the date-records... how can this behaviour be changed?

mssql:
--------
2005-11-05 3
2005-11-01 4
2005-09-10 1
null 2
null 5

pgsql:
--------
null 2
null 5
2005-11-05 3
2005-11-01 4
2005-09-10 1

thanks in advance,
thomas