1. I am in search of a simple programmer for the 8051 series. I need to be able to download a program that I compile to the chip, then pull the chip off and plug it into our test environment.
forget about the programmer, unless you plan to make 100s or 1000s of units, use ISP (In System Programming).
Depending on brand and derivative you use the standard RS232 port, a SPI cable or a JTAG cable and that is all you need plus some free software. For reference read up on FlashMagic from www.esacademy.com (Philips) or FLIP from Atmel.

2. Are the pinouts the same on the Philips 8051 and the Atmel 8051s? In other words, if I get a programmer for Philips, will it work for Atmel as well?
re programming, see above re pinouts for some yes, for some no.

3. I know C, and I also see that there are some C Compilers for the 8051 chips. Would it be easier to try and convert the code I have to C to be able to better manage the code? Are there disadvantages to using C over Assembly?
This is the eternal question and there is no absolute answer. I am opposed to converting working assembler code to C (what is the purpose) however I do write most if my new code in C. Generally speaking in most cases the slight overhead using C is many times negated by the increase in productivity. HOWEVER, since you state I will need to learn the assembly language I will say this, you will write very bad C for the '51 if you do not familiarize yourself with the assembler first "the '51 ain't no PC"

Erik