Q: Can someone give 
me advice for writing a tsr program?

 A: Writing a terminate 
and stay resident program can be considered
advanced programming and is beyond the scope of an electronic
message with limited space. Instead, here are some references to
Turbo Pascal books and papers which have a coverage of the 
subject.
Stephen O'Brien, Turbo Pascal, The Complete Reference, 
Chapter 16;
Stephen O'Brien, Turbo Pascal, Advanced Programmer's Guide, 
Chapter
6; Michael Tischer, Turbo Pascal Internals, Chapter 11 (a definite
bible of TP programming!); Michael Tischer (1992), PC Intern 
System
Programming, Chapter 32; Michael Yester, Using Turbo Pascal, 
Chapter
19; Kent Pottebaum, "Creating TSR Programs with Turbo 
Pascal", Dr.
Dobb's Journal, May 1989 and June 1989; Kris Jamsa, Dos Power 
User's
Guide, pp. 649-; Edward Mitchell (1993), Borland Pascal 
Developer's
Guide, Section "Writing TSRs", pp. 370-400, with 778 
lines of sample
code.
   Also see example code files like
ftp://garbo.uwasa.fi/pc/turboobj/tsrhelp.zip,
ftp://garbo.uwasa.fi/pc/turbopa45/tess-5.zip,
ftp://garbo.uwasa.fi/pc/turbopa45/tsrunit.zip,
ftp://garbo.uwasa.fi/pc/turbopa7/pptsr10.zip,
ftp://garbo.uwasa.fi/pc/turbopa7/tsrsrc35.zip,
ftp://garbo.uwasa.fi/pc/turbopas/deltsr.zip,
ftp://garbo.uwasa.fi/pc/turbopas/tp4_tsr.zip.