Adding additional DRAM is not going to make any difference to boot times. The biggest part of the problem has to do with how long the BIOS is taking to complete its POST processing. There are all sorts of things that could be responsible for this. It could be caused by USB devices (good or bad), DIMMs, storage devices, etc. External USB Hubs will always add to the delay as additional enumeration steps will be necessary. We also regularly see folks here asking about boot issues with some external USB HDDs. Older and higher speed DIMMs may require additional work to get initialized (try using different DIMMs to see if this makes a difference). Storage devices could have physical issues (be slowly failing; look at S.M.A.R.T. data as an indicator) or logical issues (corruption in the file system (run CHKDSK on your system drive), for example).
Hope this helps,
...S
