What is the best GPU for celeron d

A Sluggeron D is just too slow for anything modern. Go buy a Pentium 4 for like $10 if that is all your board supports.

Minimum Requirements

Dual core CPU, up from a single core at 1.4 Ghz. It looks like it may mention a Intel Pentium D rather than Intel Pentium 4.
2GB RAM (or 1GB for Windows XP), up from 1GB RAM.
The X1800 Pro (2005) is now the minimum required GPU, up from the 9500 (2002), which may no longer be supported.
The GeForce FX 5000 series (2003) also has been dropped from the minimum requirements, replaced by the 6800 (2004).
The minimum hard drive space is still 25GB.
The minimum resolution is 1024x768.


Recommended Specifications

4GB RAM, up from 2GB.
64bit Windows 7, up from 64bit Windows Vista/7.
Intel Core 2 Duo 2.2 GHz or AMD Athlon 64 X2, up from the Intel Pentium D.
Nvidia 8800GT, up from the 8600.
AMD 4830 512MB, up from the 2600.

That's the requirements for World of warcraft. Your CPU is single core, so it will not work nicely at all. You'd need a whole system upgrade, which would cost minimum around $215:
PCPartPicker part list / Price breakdown by merchant / Benchmarks

CPU: Intel Pentium G550 2.6GHz Dual-Core Processor ($34.99 @ Microcenter)
Motherboard: ASRock H61M-DGS Micro ATX LGA1155 Motherboard ($44.99 @ Amazon)
Memory: Kingston 2GB (1 x 2GB) DDR3-1333 Memory ($7.99 @ NCIX US)
Memory: Kingston 2GB (1 x 2GB) DDR3-1333 Memory ($7.99 @ NCIX US)
Storage: Western Digital Caviar Blue 500GB 3.5" 7200RPM Internal Hard Drive ($54.99 @ Microcenter)
Video Card: PowerColor Radeon HD 6670 1GB Video Card ($64.99 @ Amazon)
Total: $215.94
(Prices include shipping, taxes, and discounts when available.)

Well, he can always try it, but I really doubt it, because World of Warcraft stated any dual core CPU requirement is very modest already, considering how CPU intensive it is.