Postgres questions

Hi,

I have Debian Lenny server with Postgres 8.3 that is workin correctly, but I
have some questions about this installation.

This server is working whitout any problem but it is a little critical and I
need to know how can I do...

- I need to connect from postgres to other database (linked server) no
postgres (for example with jdbc or odbc). I have tried to work with dbi-link
with sql, it seems to work but with poor performance and whit other database
different mssql is not working. What possible options exsits with 8.3? and
with other versions?

- This server has some critical applications and I need high availability,
but I'm not sure about possible options for this versions or similar. I have
thought about active/active, active/passive or active/read-only but I'm not
sure what are real options, and what could be a possible environment for
this situation

Thanks