Looking over your code there is a few things that I can say is wrong with the way you are doing things. I will admit that I don't do a whole lot with MS SQL mixed with PHP cause MS SQL sucks.
But here is what I saw:
1. some columns in your query have spaces instead of underscores "_" that will cause issues
2. you are selecting your database in the query.
Here is what I would suggest:
1. alter your table so there are no spaces in column names
2. run this to connect
$conn = mssql_connect('server', 'username', 'password');
mssql_select_db('LIVEDATA_Dosrun', $conn);
3. now run your query (this is your same query just edited to be easier to ready and follow)
$q = "SELECT e.job_number, d.names, e.details1,
d.salesrep, s.name csr, e.due_date,
e.order_no, e.qty1, e.qty2, e.qty3, e.qty4
FROM estimate e, debtor d, salesrep s, invoice i
WHERE e.job_number = '53373'
AND i.job_no = e.job_number
AND i.csr_recnum = s.dataflex_recnum_one
AND d.ac_no = e.debtor";
4. now you can run your result
$result = mssql_query($q);
If I can be of assistance more let me know. I am always happy to help where I can.